In vitro development of resistance against antipseudomonal agents: comparison of novel β-lactam/β-lactamase inhibitor combinations and other β-lactam agents

We subjected seven P. aeruginosa isolates to a 10-day serial passaging against five antipseudomonal agents to evaluate resistance levels post-exposure and putative resistance mechanisms in terminal mutants were analyzed by whole-genome sequencing analysis. Meropenem (mean, 38-fold increase), cefepime (14.4-fold), and piperacillin-tazobactam (52.9-fold) terminal mutants displayed high minimum inhibitory concentration (MIC) values compared to those obtained after exposure to ceftolozane-tazobactam (11.4-fold) and ceftazidime-avibactam (5.7-fold). Fewer isolates developed elevated MIC values for other β-lactams and agents belonging to other classes when exposed to meropenem in comparison to other agents. Alterations in nalC and nalD, involved in the upregulation of the efflux pump system MexAB-OprM, were common and observed more frequently in isolates exposed to ceftazidime-avibactam and meropenem. These alterations, along with ones in mexR and amrR, provided resistance to most β-lactams and levofloxacin but not imipenem. The second most common gene altered was mpl, which is involved in the recycling of the cell wall peptidoglycan. These alterations were mainly noted in isolates exposed to ceftolozane-tazobactam and piperacillin-tazobactam but also in one cefepime-exposed isolate. Alterations in other genes known to be involved in β-lactam resistance (ftsI, oprD, phoP, pepA, and cplA) and multiple genes involved in lipopolysaccharide biosynthesis were also present. The data generated here suggest that there is a difference in the mechanisms selected for high-level resistance between newer β-lactam/β-lactamase inhibitor combinations and older agents. Nevertheless, the isolates exposed to all agents displayed elevated MIC values for other β-lactams (except imipenem) and quinolones tested mainly due to alterations in the MexAB-OprM regulators that extrude these agents.

Assessing the impact of meropenem exposure on ceftolozane/tazobactam-resistance development in Pseudomonas aeruginosa using in vitro serial passage

BACKGROUND

Patients infected with difficult-to-treat Pseudomonas aeruginosa are likely to receive meropenem (MEM) empirically before escalation to ceftolozane/tazobactam (C/T). We assessed whether pre-exposure to MEM affected C/T resistance development on C/T exposure.

MATERIALS AND METHODS

Nine clinical P. aeruginosa isolates were exposed to MEM 16 mg/L for 72 h. Then, isolates were serially passaged in the presence of C/T (concentration of 10 mg/L) for 72 h as two groups: an MEM-exposed group inoculated with MEM pre-exposed isolates and a non-MEM control group. At 24 h intervals, samples were plated on drug-free and drug-containing agar (C/T concentration 16/8 mg/L) and incubated to quantify bacterial densities (log10 cfu/mL). Growth on C/T agar indicated resistance development, and resistant population was calculated by dividing the cfu/mL on C/T plates by the cfu/mL on drug-free agar.

RESULTS

At 72 h, resistant populations were detected in 6/9 isolates. In five isolates, MEM exposure significantly increased the prevalence of ceftolozane/tazobactam-resistance development; the percentages of resistance population were 100%, 100%, 53.5%, 31% and 3% for the MEM-exposed versus 0%, 0%, 2%, 0.35% and ≤0.0003% in the unexposed groups. One isolate had a similar resistant population at 72 h between the two groups. The remaining isolates showed no development of resistance, regardless of previous MEM exposure.

CONCLUSIONS

MEM exposure may pre-dispose to C/T resistance development and thus limit the therapeutic utility of this β-lactam/β-lactamase inhibitor. Resistance may be a result of stress exposure or molecular-level mutations conferring cross-resistance. Further in vivo studies are needed to assess clinical implications of these findings.

Antimicrobial activity of cefepime-tazobactam combination against extended spectrum beta-lactamase and/or AmpC beta-lactamase- producing gram-negative bacilli

BACKGROUND

The problem of resistance to beta-lactam antibiotics, which is caused by ESBL and AmpC β-lactamases, is getting worse globally. Infections caused by bacterial isolates harboring these enzymes are difficult to treat with carbapenems being the sole effective treatment option for such infections. The objective of this study was to determine the frequency of ESBLs and AmpC-producing Gram-negative bacilli isolated from clinical specimens and to evaluate the sensitivity of cefepime-tazobactam combination against them.

METHODS

This is an observational cross-sectional study carried out on 100 Gram-negative bacilli at Theodor Bilharz Research Institute Hospital during the period from February 2015 to January 2016. ESBL production was screened by using the disc diffusion test followed by confirmation by the combined disc confirmatory test, the screening for AmpC production was conducted using the cefoxitin disc test, which was subsequently confirmed by the AmpC disc test. Isolates confirmed positive for ESBL and/ or AmpC production were investigated for their susceptibility to antibiotics.

RESULTS

Among 100 Gram-negative bacilli, 44 isolates were confirmed as ESBL producers by the combined disc confirmatory test out of 56 isolates that tested positive for ESBL production through the disc diffusion test. The presence of AmpC production was assessed using the cefoxitin disc test, 32 isolates were screened to be AmpC producers, and the AmpC disc test confirmed AmpC production in 9 isolates of them. Using the Mast® D68C set, 32 isolates were ESBL producers, 3 were AmpC producers, and 4 isolates were ESBL/AmpC co-producers. The highest sensitivity was to cefepime-tazobactam (91.48%) followed by the carbapenems.

CONCLUSION

Cefepime-tazobactam showed remarkable activity against ESBL and/or AmpC-producing Gram-negative bacilli and may be considered as a therapeutic alternative to carbapenems.

Identifying and mathematically modeling the time-course of extracellular metabolic markers associated with resistance to ceftolozane/tazobactam in Pseudomonas aeruginosa

Extracellular bacterial metabolites have potential as markers of bacterial growth and resistance emergence but have not been evaluated in dynamic in vitro studies. We investigated the dynamic metabolomic footprint of a multidrug-resistant hypermutable Pseudomonas aeruginosa isolate exposed to ceftolozane/tazobactam as continuous infusion (4.5 g/day, 9 g/day) in a hollow-fiber infection model over 7-9 days in biological replicates (n = 5). Bacterial samples were collected at 0, 7, 23, 47, 71, 95, 143, 167, 191, and 215 h, the supernatant quenched, and extracellular metabolites extracted. Metabolites were analyzed via untargeted metabolomics, including hierarchical clustering and correlation with quantified total and resistant bacterial populations. The time-courses of five (of 1,921 detected) metabolites from enriched pathways were mathematically modeled. Absorbed L-arginine and secreted L-ornithine were highly correlated with the total bacterial population (r -0.79 and 0.82, respectively, P<0.0001). Ribose-5-phosphate, sedoheptulose-7-phosphate, and trehalose-6-phosphate correlated with the resistant subpopulation (0.64, 0.64, and 0.67, respectively, P<0.0001) and were likely secreted due to resistant growth overcoming oxidative and osmotic stress induced by ceftolozane/tazobactam. Using pharmacokinetic/pharmacodynamic-based transduction models, these metabolites were successfully modeled based on the total or resistant bacterial populations. The models well described the abundance of each metabolite across the differing time-course profiles of biological replicates, based on bacterial killing and, importantly, resistant regrowth. These proof-of-concept studies suggest that further exploration is warranted to determine the generalizability of these findings. The metabolites modeled here are not exclusive to bacteria. Future studies may use this approach to identify bacteria-specific metabolites correlating with resistance, which would ultimately be extremely useful for clinical translation.

Identification of a CTX-M-255 β-lactamase containing a G239S substitution selectively conferring resistance to penicillin/β-lactamase inhibitor combinations

OBJECTIVES

An Escherichia coli isolate, WGS1363, showed resistance to piperacillin/tazobactam but susceptibility to cephalosporins and contained a previously unrecognized β-lactamase, CTX-M-255, as the only acquired β-lactamase. CTX-M-255 was identical to CTX-M-27 except for a G239S substitution. Here, we characterize the hydrolytic spectrum of CTX-M-255 and a previously reported β-lactamase, CTX-M-178, also containing a G239S substitution and compare it to their respective parental enzymes, CTX-M-27 and CTX-M-15.

METHODS

All β-lactamase genes were expressed in E. coli TOP10 and MICs to representative β-lactam-antibiotics were determined. Furthermore, blaCTX-M-15,  blaCTX-M-27, blaCTX-M-178 and blaCTX-M-255 with C-terminal His-tag fusions were affinity purified for enzyme kinetic assays determining Michaelis-Menten kinetic parameters against representative β-lactam-antibiotics and IC50s of clavulanate, sulbactam, tazobactam and avibactam.

RESULTS

TOP10-transformants expressing blaCTX-M-178 and blaCTX-M-255 showed resistance to penicillin/β-lactamase combinations and susceptibility to cephalothin and cefotaxime in contrast to transformants expressing blaCTX-M-15 and blaCTX-M-27. Determination of enzyme kinetic parameters showed that CTX-M-178 and CTX-M-255 both lacked hydrolytic activity against cephalosporins and showed impaired hydrolytic efficiency against penicillin antibiotics compared to their parental enzymes. Both enzymes appeared more active against piperacillin compared to benzylpenicillin and ampicillin. Compared to their parental enzymes, IC50s of β-lactamase-inhibitors were increased more than 1000-fold for CTX-M-178 and CTX-M-255.

CONCLUSIONS

CTX-M-178 and CTX-M-255, both containing a G239S substitution, conferred resistance to piperacillin/tazobactam and may be characterized as inhibitor-resistant CTX-M β-lactamases. Inhibitor resistance was accompanied by loss of activity against cephalosporins and monobactams. These findings add to the necessary knowledge base for predicting antibiotic susceptibility from genotypic data.

Clinical outcomes of intensive care unit patients infected with multidrug-resistant gram-negative bacteria treated with ceftazidime/avibactam and ceftolozane/tazobactam

In intensive care units (ICUs), infection rates range from 18 to 54%, which is five to ten times higher than those observed in other hospital units, with a mortality rate of 9% to 60%. In recent decades, the susceptibility pattern has changed and Gram-Negative Bacteria (GNB) have become a threat due to their high frequency of multidrug resistance associated with a scarcity of therapeutic options. However, the drugs Ceftolozane/Tazobactam (C/T) and Ceftazidime/Avibactam (C/A) are demonstrating good clinical and microbiological response in the treatment of severe nosocomial infections. Therefore, this study aims to evaluate the clinical outcome of patients with severe infections caused by Multidrug-Resistant (MDR) GNB treated with C/T and C/A. Our study evaluates a total of 131 patients who received treatment with C/T and C/A due to infections caused by MDR GNB within the period from 2018 to 2021. The main infections were urinary tract (46,6%) and respiratory (26,7%) infections. Pseudomonas aeruginosa was the prevailing agent in the sample evaluation (34.3%), followed by Klebsiella pneumoniae (30,1%). About 54,9% of patients showed a favorable response, with culture negativation in 66,4% of the samples, with no discrepancy in negativations when comparing ages: 67,7% in young and 66% in elderly patients. Among the patients, 62,6% received monotherapy with C/T and C/A with a better response observed with monotherapy compared to combination therapy (58,6% vs 41,4%). The overall mortality rate was 45%, with MDR GNB infections responsible for 33,9% of these deaths, and the others (66,1%) due to factors such as oncological, hematological, and degenerative neurological diseases. In regards to hematological aspect, 35,1% of patients showed changes, with 28,2% of them presenting anemia, 4,5% thrombocytopenia, and 2,5% thrombocytosis. Concerning the use of invasive devices, higher mortality was observed in patients on mechanical ventilation (52%). In this manner, it was possible to observe that therapy with C/T and C/A yielded a favorable clinical outcome in patients with severe infections caused by MDR GNB in the study. These drugs also demonstrated good tolerability regardless of age or the presence of preexisting comorbidities and were deemed safe when assessing adverse effects. Our data also demonstrate the importance of determining the mechanism of resistance to carbapenems so that these drugs can be used more effectively and rationally.

Activity of imipenem/relebactam and comparators against KPC-producing Klebsiella pneumoniae and imipenem-resistant Pseudomonas aeruginosa

PURPOSE

Relebactam is a novel β-lactamase inhibitor, which, when combined with imipenem/cilastatin, is active against both class A and class C β-lactamases. To evaluate in vitro antimicrobial activity of imipenem/relebactam against a collection of recent clinical isolates of carbapenem-non-susceptible P. aeruginosa and K. pneumoniae ST258 and ST512 KPC producers belonging to different lineages from hospitals in Southern Spain.

METHODS

Six hundred and seventy-eight isolates were tested: 265 K. pneumoniae (230 ST512/KPC-3 and 35 ST258/KPC-3) and 413 carbapenem-non-susceptible P. aeruginosa. Imipenem, piperacillin/tazobactam, ceftazidime, cefepime, aztreonam, ceftolozane/tazobactam, meropenem, amikacin, ciprofloxacin, colistin, and ceftazidime/avibactam were used as comparators against P. aeruginosa. Against K. pneumoniae ceftazidime, cefepime, aztreonam, and ceftolozane/tazobactam were not tested, and tigecycline was studied instead. MICs were determined in duplicate by broth microdilution according to EUCAST guidelines.

RESULTS

Imipenem/relebactam displayed potent in vitro activity against both sequence types of KPC-3-producing K. pneumoniae. MIC50 and MIC90 values were 0.25 mg/L and 1 mg/L, respectively, with percent of susceptible isolates >97%. Only three K. pneumoniae ST512/KPC-3 isolates and one ST258/KPC-3 were resistant to imipenem/relebactam. Relebactam sensitized 98.5% of K. pneumoniae isolates resistant to imipenem. The activity of imipenem/relebactam against P. aeruginosa was moderate (susceptibility rate: 62.7%). Analysis of the acquired and mutational resistome of isolates with high levels of resistance to imipenem/relebactam has not shown a clear association between them.

CONCLUSION

Imipenem/relebactam showed excellent activity against K. pneumoniae KPC-3. The activity of imipenem/relebactam against imipenem-resistant P. aeruginosa was moderate.

Evaluation of three commercial methods of susceptibility testing for ceftolozane/tazobactam against carbapenem-resistant Pseudomonas aeruginosa

INTRODUCTION

Ceftolozane/tazobactam has shown excellent activity against Pseudomonas aeruginosa, but this drug is not always included in commercial panels. The aim of the study was to evaluate the performance of 2 gradient strips (BioMérieux and Liofilchem) and a commercial microdilution panel (Sensititre, EURGNCOL panel) using this combination against carbapenem-resistant P. aeruginosa isolates.

METHODS

Three commercial methods were tested with 41 metallo-beta-lactamase-producing and 59 non-carbapenemase-producing P. aeruginosa isolates. Broth microdilution was used as reference.

RESULTS

All carbapenemase-producing isolates and only one non-producing isolate were resistant to this antibiotic. Both essential agreement and bias were outside the acceptance intervals since MIC values were higher than reference values for all three methods. The Kappa index indicated poor or weak agreement. Changes in clinical categories were observed in 3 isolates.

CONCLUSIONS

The three methods yielded poor agreement with the reference. Despite the differences in MIC values, fewer than 3% involved category changes.

Characterization of Pseudomonas aeruginosa resistance to ceftolozane-tazobactam due to ampC and/or ampD mutations observed during treatment using semi-mechanistic PKPD modeling

A double ampC (AmpCG183D) and ampD (AmpDH157Y) genes mutations have been identified by whole genome sequencing in a Pseudomonas aeruginosa (PaS) that became resistant (PaR) in a patient treated by ceftolozane/tazobactam (C/T). To precisely characterize the respective contributions of these mutations on the decreased susceptibility to C/T and on the parallel increased susceptibility to imipenem (IMI), mutants were generated by homologous recombination in PAO1 reference strain (PAO1- AmpCG183D, PAO1-AmpDH157Y, PAO1-AmpCG183D/AmpDH157Y) and in PaR (PaR-AmpCPaS/AmpDPaS). Sequential time-kill curve experiments were conducted on all strains and analyzed by semi-mechanistic PKPD modeling. A PKPD model with adaptation successfully described the data, allowing discrimination between initial and time-related (adaptive resistance) effects of mutations. With PAO1 and mutant-derived strains, initial EC50 values increased by 1.4, 4.1, and 29-fold after AmpCG183D , AmpDH157Y and AmpCG183D/AmpDH157Y mutations, respectively. EC50 values were increased by 320, 12.4, and 55-fold at the end of the 2 nd experiment. EC50 of PAO1-AmpCG183D/AmpDH157Y was higher than that of single mutants at any time of the experiments. Within the PaR clinical background, reversal of AmpCG183D, and AmpDH157Y mutations led to an important decrease of EC50 value, from 80.5 mg/L to 6.77 mg/L for PaR and PaR-AmpCPaS/AmpDPaS, respectively. The effect of mutations on IMI susceptibility mainly showed that the AmpCG183D mutation prevented the emergence of adaptive resistance. The model successfully described the separate and combined effect of AmpCG183D and AmpDH157Y mutations against C/T and IMI, allowing discrimination and quantification of the initial and time-related effects of mutations. This method could be reproduced in clinical strains to decipher complex resistance mechanisms.

EUCAST rapid antimicrobial susceptibility testing (RAST) compared to conventional susceptibility testing: implementation and potential added value in a tertiary hospital in Belgium

OBJECTIVES

EUCAST breakpoints for short incubation disk diffusion allow rapid antimicrobial susceptibility testing (RAST) directly from positive blood cultures. We evaluate the RAST methodology and assess its potential added value in a setting of low prevalence of multidrug-resistant (MDR) organisms.

METHODS

In our two-part study, we performed RAST on 127 clinical blood cultures at 6 and 8 h and determined categorical agreement with direct susceptibility testing. We also measure the impact of susceptibility results on antimicrobial therapy compared to empirical treatment.

RESULTS

Categorical agreement was 96.2% at 6 h (575/598 isolate-drug combinations) and 96.6% at 8 h (568/588 combinations). Major errors involved piperacillin/tazobactam in 16 of 31 cases. The second part of our study shows that AST reporting proved essential in correcting ineffective empirical therapy in 6.3% of the patients (8/126).

CONCLUSION

EUCAST RAST is an inexpensive and reliable method of susceptibility testing, although care must be taken with reporting piperacillin/tazobactam. In support of RAST implementation, we show that AST remains of great importance in providing effective therapy, even in a setting of low MDR prevalence and elaborate antibiotic guidelines.

In vitro efficacy of humanized regimen of flomoxef against extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae

This study compared the efficacy of flomoxef with other β-lactam antibiotics against extended-spectrum β-lactamases (ESBL)-producing bacteria of clinical relevance. First, the prevalence and β-lactamase genotypes of ESBL-producing strains among Escherichia coli and Klebsiella pneumoniae isolates collected in Japan from 2004 to 2018 were investigated. High MIC90 values (>64 µg/mL) of ceftriaxone, cefepime, and ceftazidime and low MIC90 values (≤0.06-2 µg/mL) of flomoxef, cefmetazole, and meropenem against both species were observed. Second, a chemostat model was used to analyze the efficacy of humanized regimens of three oxacephem/cephamycin antibiotics (flomoxef, cefmetazole, cefoxitin) and two other antibiotics (meropenem and piperacillin/tazobactam) in suppressing the growth of five ESBL-producing E. coli and two K. pneumoniae strains. Flomoxef, piperacillin/tazobactam, and meropenem showed good bactericidal effects with >4 log10 CFU/mL reduction without bacterial regrowth at 24 h even when the MIC of test isolates was >MIC90. Cefmetazole and cefoxitin resulted in regrowth of test isolates with MIC ≥MIC90 at 24 h. Cefmetazole, cefoxitin, flomoxef, and meropenem showed increased MICs for regrown samples. A clear relationship between the proportion of time that the free drug concentration exceeded the MIC (%fT>MIC) and antibiotic efficacy was found for flomoxef, cefoxitin, and cefmetazole, and flomoxef had the highest %fT>MIC, whereas discrepancies between Clinical and Laboratory Standards Institute breakpoint and bactericidal activity were observed for cefmetazole. Flomoxef was effective in preventing the growth of all ESBL-producing strains, even those with an MIC eight times the MIC90. Thus, flomoxef may be a good alternative to meropenem in context of carbapenems sparing stewardship.

Temporal and geographical prevalence of carbapenem-resistant Pseudomonas aeruginosa and the in vitro activity of ceftolozane/tazobactam and comparators in Taiwan-SMART 2012-2021

OBJECTIVES

To determine the in vitro activities of ceftolozane/tazobactam (C/T) and comparators against Pseudomonas aeruginosa isolates cultured from hospitalised patient samples in Taiwan from 2012 to 2021 with an additional focus on the temporal and geographical prevalence of carbapenem-resistant P. aeruginosa (CRPA).

METHODS

P. aeruginosa isolates (n = 3013) were collected annually by clinical laboratories in northern (two medical centres), central (three medical centres), and southern Taiwan (four medical centres) as part of the SMART global surveillance program. MICs were determined by CLSI broth microdilution and interpreted using 2022 CLSI breakpoints. Molecular β-lactamase gene identification was performed on selected non-susceptible isolate subsets in 2015 and later.

RESULTS

Overall, 520 (17.3%) CRPA isolates were identified. The prevalence of CRPA increased from 11.5%-12.3% (2012-2015) to 19.4%-22.8% (2018-2021) (P ≤ 0.0001). Medical centres in northern Taiwan reported the highest percentages of CRPA. C/T, first tested in the SMART program in 2016, was highly active against all P. aeruginosa (97% susceptible), with annual susceptibility rates ranging from 94% (2017) to 99% (2020). Against CRPA, C/T inhibited >90% of isolates each year, with the exception of 2017 (79.4% susceptible). Most CRPA isolates (83%) were molecularly characterised, and only 2.1% (9/433) carried a carbapenemase (most commonly, VIM); all nine carbapenemase-positive isolates were from northern and central Taiwan.

CONCLUSION

The prevalence of CRPA increased significantly in Taiwan from 2012 to 2021 and warrants continued monitoring. In 2021, 97% of all P. aeruginosa and 92% of CRPA in Taiwan were C/T susceptible. Routine in vitro susceptibility testing of clinical isolates of P. aeruginosa against C/T, and other newer β-lactam/β-lactamase inhibitor combinations, appears prudent.

Ceftolozane-Tazobactam against Pseudomonas aeruginosa Cystic Fibrosis Clinical Isolates in the Hollow-Fiber Infection Model: Challenges Imposed by Hypermutability and Heteroresistance

Pseudomonas aeruginosa remains a challenge in chronic respiratory infections in cystic fibrosis (CF). Ceftolozane-tazobactam has not yet been evaluated against multidrug-resistant hypermutable P. aeruginosa isolates in the hollow-fiber infection model (HFIM). Isolates CW41, CW35, and CW44 (ceftolozane-tazobactam MICs of 4, 4, and 2 mg/L, respectively) from adults with CF were exposed to simulated representative epithelial lining fluid pharmacokinetics of ceftolozane-tazobactam in the HFIM. Regimens were continuous infusion (CI; 4.5 g/day to 9 g/day, all isolates) and 1-h infusions (1.5 g every 8 hours and 3 g every 8 hours, CW41). Whole-genome sequencing and mechanism-based modeling were performed for CW41. CW41 (in four of five biological replicates) and CW44 harbored preexisting resistant subpopulations; CW35 did not. For replicates 1 to 4 of CW41 and CW44, 9 g/day CI decreased bacterial counts to <3 log10 CFU/mL for 24 to 48 h, followed by regrowth and resistance amplification. Replicate 5 of CW41 had no preexisting subpopulations and was suppressed below ~3 log10 CFU/mL for 120 h by 9 g/day CI, followed by resistant regrowth. Both CI regimens reduced CW35 bacterial counts to <1 log10 CFU/mL by 120 h without regrowth. These results corresponded with the presence or absence of preexisting resistant subpopulations and resistance-associated mutations at baseline. Mutations in ampC, algO, and mexY were identified following CW41 exposure to ceftolozane-tazobactam at 167 to 215 h. Mechanism-based modeling well described total and resistant bacterial counts. The findings highlight the impact of heteroresistance and baseline mutations on the effect of ceftolozane-tazobactam and limitations of MIC to predict bacterial outcomes. The resistance amplification in two of three isolates supports current guidelines that ceftolozane-tazobactam should be utilized together with another antibiotic against P. aeruginosa in CF.

In Vitro Susceptibility of Achromobacter Species Isolated from Cystic Fibrosis Patients: a 6-Year Survey

We conducted in vitro antimicrobial susceptibility testing of 267 Achromobacter isolates for 16 antibiotics from 2017 to 2022. The highest susceptibility was found for piperacillin-tazobactam (70%) and ceftazidime-avibactam (62%). Between 30% and 49% of strains were susceptible to tigecycline, ceftazidime, and meropenem. We applied species-specific Achromobacter xylosoxidans breakpoints for piperacillin-tazobactam, meropenem, and trimethoprim-sulfamethoxazole and EUCAST pharmacokinetic/pharmacodynamic (PK/PD) breakpoints for the others. A. xylosoxidans was the most frequently isolated species, followed by Achromobacter insuavis and Achromobacter ruhlandii.

Comparison of In Vitro Activity of Ceftazidime-Avibactam and Imipenem-Relebactam against Clinical Isolates of Pseudomonas aeruginosa

The role of novel β-lactam/β-lactamase inhibitor combinations in ceftazidime-nonsusceptible (CAZ-NS) and imipenem-nonsusceptible (IPM-NS) Pseudomonas aeruginosa has not been fully elucidated. This study evaluated the in vitro activity of novel β-lactam/β-lactamase inhibitor combinations against Pseudomonas aeruginosa clinical isolates, determined how avibactam restored ceftazidime activity, and compared the activity of ceftazidime-avibactam (CZA) and imipenem-relebactam (IMR) against KPC-producing P. aeruginosa. Similar high susceptibility rates for CZA, IMR, and ceftolozane-tazobactam (88.9% to 89.8%) were found for 596 P. aeruginosa clinical isolates from 11 hospitals in China, and a higher susceptibility rate to ceftazidime than imipenem was observed (73.5% versus 63.1%). For CAZ-NS and IPM-NS isolates, susceptibility rates for CZA, ceftolozane-tazobactam, and IMR were 61.5% (75/122), 54.9% (67/122), and 51.6% (63/122), respectively. For CAZ-NS, IPM-NS but CZA-susceptible isolates, 34.7% (26/75) harbored acquired β-lactamases with KPC-2 predominant (n = 19), and 45.3% (34/75) presented overexpression of chromosomal β-lactamase ampC. Among 22 isolates carrying KPC-2 carbapenemase alone, susceptibility rates to CZA and IMR were 86.4% (19/22) and 9.1% (2/22), respectively. Notably, 95% (19/20) of IMR-nonsusceptible isolates had an inactivating mutation of oprD gene. In conclusion, CZA, ceftolozane-tazobactam, and IMR exhibit high activity against P. aeruginosa, and CZA is more active than IMR against CAZ-NS and IPM-NS isolates as well as KPC-producing P. aeruginosa. Avibactam overcomes ceftazidime resistance engendered by KPC-2 enzyme and overexpressed AmpC. IMPORTANCE The emergence of antimicrobial resistance poses a particular challenge globally, and the concept of P. aeruginosa with "difficult-to-treat" resistance (DTR-P. aeruginosa) was proposed. Here, P. aeruginosa clinical isolates were highly susceptible to three β-lactamase inhibitor combinations, CZA, IMR, and ceftolozane-tazobactam. The combination of KPC-2 enzyme and nonfunctional porin OprD contributed to IMR resistance in P. aeruginosa, and CZA was more active than IMR in fighting against KPC-2-producing P. aeruginosa. CZA also showed good activity against CAZ-NS and IPM-NS P. aeruginosa, primarily by inhibiting KPC-2 enzyme and overproduced AmpC, supporting the clinical use of CZA in the treatment of infections caused by DTR-P. aeruginosa.

Comparative in vitro antipseudomonal activity of ceftolozane/tazobactam against Pseudomonas aeruginosa isolates from children with cystic fibrosis

This study evaluated the in vitro activity of Ceftolozane/tazobactam (C/T) vs 10 comparator agents against Pseudomonas aeruginosa isolates obtained from clinical respiratory samples from pediatric patients with cystic fibrosis at three hospitals during 2015 to 2020. Antimicrobial susceptibility testing was performed using microbroth dilution technique with custom prepared Sensititre® MIC plates. MICs were determined via Sensititre Vizion® system and results were interpreted using current CLSI and EUCAST (2022) breakpoint criteria. C/T was the most potent agent as compared with other antipseudomonal drugs against 291 isolates with MIC₅₀ = 1 μg/mL and MIC₉₀ = 2 μg/mL with percent susceptibility as 95.2%. C/T remained active against majority of ß-lactam non-susceptible isolates; percent susceptibility ranging from 61.2% to 80% including 65.9% ceftazidime non-susceptible isolates. C/T had high activity against P. aeruginosa from 3 geographically diverse pediatric medical centers. Study results suggest that C/T may be used as a potential therapeutic option for treating pediatric patients with CF.

Prevalence of Multidrug Resistant Pseudomonas aeruginosa Isolated from Clinical Specimens in Tertiary Care Hospital

BACKGROUND

Pseudomonas aeruginosa is an opportunistic pathogen, which causes nosocomial infections in human. The rapid increase in drug resistance of this pathogen is a global concern. The aim of this study was to determine the clinical burden of P.aeruginosa, its antibiotic susceptibility pattern along with metallo-β-lactamase (MBL) detection.

METHODS

The descriptive cross-sectional study was conducted in Upendra Devkota Memorial National Institute of Neurological and Allied Sciences from January to August 2021. Isolation and identification of P. aeruginosa from clinical specimens was performed by using standard laboratory procedure. All bacterial isolates were phenotypically screened for multidrug resistance using Kirby Bauer disc diffusion method. All the multidrug resistant P.aeruginosa were phenotypically screened for MBL producer by Imipenem-EDTA combined disc diffusion test (CDDT).

RESULTS

A total of 770 samples were processed of which 36 isolates of P. aeruginosa were obtained. P.aeruginosa was isolated mainly from tracheal aspirates, sputum, blood and urine. Among 36 isolates, 50% were found to be multidrug resistant (MDR). More percentage of P.aeruginosa isolates were found resistant to aztreonam, ofloxacin and levofloxacin (52.8%). Furthermore, this study reveals antibiotics like piperacillin/tazobactam and carbapenem were found to be good choice for the treatment of infection caused by this organism. Among MDR isolates 66.7% were found to be MBL producer.

CONCLUSIONS

The data in this study highlights the prevalence of multidrug resistant, MBL producer, and colistin resistant P.aeruginosa in clinical specimens. In this study, carbapenems and piperacillin/tazobactam were found to be most effective antimicrobial drugs for empirical therapy in P.aeruginosa infections.

Satisfactory In Vitro Activity of Ceftolozane–Tazobactam against Carbapenem-Resistant Pseudomonas aeruginosa But Not against Klebsiella pneumoniae Isolates

Background: Gram-negative rods are one of the most commonly isolated bacteria within human infections. These microorganisms are typically opportunistic pathogens that pose a serious threat to public health due to the possibility of transmission in the human population. Resistance to carbapenems is one of the most important antimicrobial resistance mechanisms amongst them. The aim of this study was to evaluate ceftolozane–tazobactam in vitro activity against carbapenem-resistant Pseudomonas aeruginosa and Klebsiella pneumoniae clinical strains. Information on the antimicrobial activity of this antimicrobial against Gram-negative rods was also supplemented with a brief review of the relevant literature. Methods: The research involved 316 strains of Gram-negative rods: P. aeruginosa—206 and K. pneumoniae—110. Results: Of the tested strains, 86.0% P. aeruginosa and 30.0% K. pneumoniae remained susceptible to ceftolozane–tazobactam. Conclusions: Therefore, ceftolozane–tazobactam might be a good option in the treatment of infections caused by carbapenem-resistant P. aeruginosa strains, including those in ICU patients. Meanwhile, due to dissemination of ESBLs among K. pneumoniae strains, infections with this etiology should not be treated with the ceftolozane–tazobactam combination.

Evaluation of ceftolozane-tazobactam susceptibility on a French nationwide collection of Enterobacterales

OBJECTIVES

Ceftolozane-tazobactam (C/T) proved its efficacy for the treatment of infections caused by non-carbapenemase producing Pseudomonas aeruginosa and Enterobacterales. Here, we aimed to provide susceptibility data on a large series of Enterobacterales since the revision of EUCAST categorization breakpoints in 2020.

METHODS

First, C/T susceptibility was determined on characterized Enterobacterales resistant to third generation cephalosporins (3GCs) (extended spectrum β-lactamase [ESBL] production or different levels of AmpC overexpression) (n = 213) and carbapenem-resistant Enterobacterales (CRE) (n = 259), including 170 carbapenemase producers (CPE). Then, 1632 consecutive clinical Enterobacterales responsible for infection were prospectively collected in 23 French hospitals. C/T susceptibility was determined by E-test® (biomérieux) and broth microdilution (BMD) (Sensititre™, Thermo Scientific) to perform method comparison.

RESULTS

Within the collection isolates, 88% of 3GC resistant strains were susceptible to C/T, with important variation depending on the resistance mechanism: 93% vs. 13% susceptibility for CTX-M and SHV-ESBL producers, respectively. Only 20% of the CRE were susceptible to C/T. Among CPE, 80% of OXA-48-like producers were susceptible to C/T, whereas all metallo-β-lactamase producers were resistant. The prospective study revealed that 95.6% of clinical isolates were susceptible to C/T. Method comparison performed on these 1632 clinical isolates demonstrated 99% of categorization agreement between MIC to C/T determined by E-test® in comparison with the BMD (reference) and only 74% of essential agreement.

CONCLUSION

Overall, C/T showed good activity against wild-type Enterobacterales, AmpC producers, and ESBL-producing Escherichia coli but is less active against ESBL-producing Klebsiella pneumoniae, and CRE. E-test® led to an underestimation of the MICs in comparison to the BMD reference.

Activity of ceftolozane/tazobactam and imipenem/relebactam against clinical gram-negative isolates from Czech Republic, Hungary, and Poland-SMART 2017-2020

Antimicrobial susceptibility was determined for clinical gram-negative isolates from Czech Republic, Hungary, and Poland, where published data for ceftolozane/tazobactam (C/T) and imipenem/relebactam (IMI/REL) is scarce. C/T was active against 94.3% of Enterobacterales, 10-18% higher than the tested cephalosporins and piperacillin/tazobactam. IMI/REL was the most active tested agent against non-Morganellaceae Enterobacterales (99.7% susceptible). C/T was the most active among all studied agents except colistin against Pseudomonas aeruginosa (96.0% susceptible); susceptibility to IMI/REL was 90.7%. C/T maintained activity against 73.7-85.3% of β-lactam-resistant or multidrug-resistant P. aeruginosa subsets. C/T and IMI/REL could represent important treatment options for patients from these countries.

Antimicrobial Activity of Ceftazidime-Avibactam, Ceftolozane-Tazobactam, Cefiderocol, and Novel Darobactin Analogs against Multidrug-Resistant Pseudomonas aeruginosa Isolates from Pediatric and Adolescent Cystic Fibrosis Patients

The emergence and spread of antimicrobial resistance (AMR) in Gram-negative pathogens, such as carbapenem-resistant Pseudomonas aeruginosa, pose an increasing threat to health care. Patients with immunodeficiencies or chronic pulmonary disease, like cystic fibrosis (CF), are particularly vulnerable to Pseudomonas infections and depend heavily on antibiotic therapy. To broaden limited treatment options, this study evaluated the potency of the recently licensed drugs ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), and cefiderocol (FDC) as well as two novel preclinical antibiotics, darobactins B (DAR B) and B9 (DAR B9), against clinical P. aeruginosa isolates derived from respiratory samples of CF patients. We observed high levels of resistance to all three newly licensed drugs, with cefiderocol exhibiting the best activity. From the 66 investigated P. aeruginosa isolates, a total of 53% were resistant to CZA, 49% to C/T, and 30% to FDC. Strikingly, 52 of the evaluated isolates were obtained from CF patients prior to market introduction of the drugs. Thus, our results suggest that resistance to CZA, C/T, and FDC may be due to preexisting resistance mechanisms. On the other hand, our two novel preclinical compounds performed better than (CZA and C/T) or close to (FDC) the licensed drugs-most likely due to the novel mode of action. Thus, our results highlight the necessity of global consistency in the area of antibiotic stewardship to prevent AMR from further impairing the potency of antibiotics in clinical practice. Ultimately, this study demonstrates the urgency to support the development of novel antimicrobials, preferably with a new mode of action such as darobactins B and B9, two very promising antimicrobial compounds for the treatment of critically ill patients suffering from multidrug-resistant Gram-negative (MRGN) infections. IMPORTANCE Antimicrobial resistance (AMR) represents an ever increasing threat to the health care system. Even recently licensed drugs are often not efficient for the treatment of infections caused by Gram-negative bacteria, like Pseudomonas aeruginosa, a causative agent of lung infections. To address this unmet medical need, innovative antibiotics, which possess a new mode of action, need to be developed. Here, the antibiogram of clinical isolates derived from cystic fibrosis patients was generated and new bicyclic heptapeptides, which inhibit the outer membrane protein BamA, exhibited strong activity, also against multidrug-resistant isolates.

Comparative activity of newer β-lactam/β-lactamase inhibitor combinations against Pseudomonas aeruginosa isolates from US medical centres (2020-2021)

OBJECTIVES

To evaluate the in-vitro activity of ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, imipenem-relebactam and comparator agents against contemporary Pseudomonas aeruginosa isolates from US hospitals.

METHODS

In total, 3184 isolates were collected consecutively from 71 US medical centres in 2020-2021, and susceptibility tested by reference broth microdilution. Clinical Laboratory Standard Institute breakpoints were applied.

RESULTS

Ceftazidime-avibactam [97.0% susceptible (S)], ceftolozane-tazobactam (98.0%S), imipenem-relebactam (97.3%S) and tobramycin (96.4%S) were the most active agents against the aggregate P. aeruginosa isolate collection, and retained good activity against piperacillin-tazobactam-non-susceptible, meropenem-non-susceptible and multi-drug-resistant (MDR) isolates. All other antimicrobials tested showed limited activity against piperacillin-tazobactam-non-susceptible, meropenem-non-susceptible and MDR isolates. The most common infections were pneumonia (45.9%), skin and skin structure infections (19.0%), urinary tract infections (17.0%) and bloodstream infections (11.7%); ceftazidime-avibactam, ceftolozane-tazobactam and imipenem-relebactam showed consistent activity against isolates from these infection types. Susceptibility to piperacillin-tazobactam and meropenem was lower among isolates from pneumonia compared with other infection types.

CONCLUSIONS

Ceftazidime-avibactam, ceftolozane-tazobactam and imipenem-relebactam were highly active, and exhibited similar coverage against a large contemporary collection of P. aeruginosa isolates from US hospitals. Cross-resistance among the newer β-lactams/β-lactam inhibitors (BL/BLIs) varied markedly; ≥72.1% of isolates resistant to one of the three newer BL/BLIs approved for P. aeruginosa treatment remained susceptible to at least one of the other two BL/BLIs, indicating that all three should be tested in the clinical laboratory. These three BL/BLIs represent valuable therapeutic options for P. aeruginosa infection.

In Vitro Activity of Cefepime-Taniborbactam and Comparators against Clinical Isolates of Gram-Negative Bacilli from 2018 to 2020: Results from the Global Evaluation of Antimicrobial Resistance via Surveillance (GEARS) Program

Taniborbactam is a novel cyclic boronate β-lactamase inhibitor in clinical development in combination with cefepime. We assessed the in vitro activity of cefepime-taniborbactam and comparators against a 2018-2020 collection of Enterobacterales (n = 13,731) and Pseudomonas aeruginosa (n = 4,619) isolates cultured from infected patients attending hospitals in 56 countries. MICs were determined by CLSI broth microdilution. Taniborbactam was tested at a fixed concentration of 4 μg/mL. Isolates with cefepime-taniborbactam MICs of ≥16 μg/mL underwent whole-genome sequencing. β-lactamase genes were identified in meropenem-resistant isolates by PCR/Sanger sequencing. Against Enterobacterales, taniborbactam reduced the cefepime MIC90 value by >64-fold (from >16 to 0.25 μg/mL). At ≤16 μg/mL, cefepime-taniborbactam inhibited 99.7% of all Enterobacterales isolates; >97% of isolates with multidrug-resistant (MDR) and ceftolozane-tazobactam-resistant phenotypes; ≥90% of isolates with meropenem-resistant, difficult-to-treat-resistant (DTR), meropenem-vaborbactam-resistant, and ceftazidime-avibactam-resistant phenotypes; 100% of VIM-positive, AmpC-positive, and KPC-positive isolates; 98.7% of extended-spectrum β-lactamase (ESBL)-positive; 98.8% of OXA-48-like-positive; and 84.6% of NDM-positive isolates. Against P. aeruginosa, taniborbactam reduced the cefepime MIC90 value by 4-fold (from 32 to 8 μg/mL). At ≤16 μg/mL, cefepime-taniborbactam inhibited 97.4% of all P. aeruginosa isolates; ≥85% of isolates with meropenem-resistant, MDR, and meropenem-vaborbactam-resistant phenotypes; >75% of isolates with DTR, ceftazidime-avibactam-resistant, and ceftolozane-tazobactam-resistant phenotypes; and 87.4% of VIM-positive isolates. Multiple potential mechanisms, including carriage of IMP, certain alterations in PBP3, permeability (porin) defects, and possibly, upregulation of efflux were present in most isolates with cefepime-taniborbactam MICs of ≥16 μg/mL. We conclude that cefepime-taniborbactam exhibited potent in vitro activity against Enterobacterales and P. aeruginosa and inhibited most carbapenem-resistant isolates, including those carrying serine carbapenemases or NDM/VIM metallo-β-lactamases (MBLs).

Phenotypic and genotypic profile of ceftolozane/tazobactam-non-susceptible, carbapenem-resistant Pseudomonas aeruginosa

OBJECTIVES

To evaluate the genotypic and ceftazidime/avibactam-susceptibility profiles amongst ceftolozane/tazobactam-non-susceptible (NS), MBL-negative Pseudomonas aeruginosa in a global surveillance programme.

METHODS

Isolates were collected as part of the ERACE-PA Global Surveillance programme. Carbapenem-resistant P. aeruginosa deemed clinically relevant by the submitting laboratories were included. Broth microdilution MICs were conducted per CLSI standards to ceftolozane/tazobactam, ceftazidime/avibactam, ceftazidime and cefepime. Genotypic carbapenemases were detected using CarbaR and CarbaR NxG (research use only). Isolates negative for carbapenemases by PCR were assessed via WGS. Isolates were included in the analysis if they were ceftolozane/tazobactam-NS and lacked detection of known MBLs.

RESULTS

Of the 807 isolates collected in the ERACE-PA programme, 126 (16%) were ceftolozane/tazobactam-NS and lacked MBLs. Cross-resistance to ceftazidime and cefepime was common, with only 5% and 16% testing susceptible, respectively. Ceftazidime/avibactam retained in vitro activity, with 65% of isolates testing susceptible. GES was the most common enzymology, detected in 57 (45%) isolates, and 89% remained susceptible to ceftazidime/avibactam. Seven isolates harboured KPC and all tested susceptible to ceftazidime/avibactam. In the remaining 62 isolates, WGS revealed various ESBLs or OXA β-lactamases. While 39% remained susceptible to ceftazidime/avibactam, marked variability was observed among the diverse resistance mechanisms.

CONCLUSIONS

Ceftazidime/avibactam remained active in vitro against the majority of ceftolozane/tazobactam-NS, MBL-negative P. aeruginosa. Ceftazidime/avibactam was highly active against isolates harbouring GES and KPC β-lactamases. These data highlight the potential clinical utility of genotypic profiling as well as the need to test multiple novel agents when carbapenem-resistant P. aeruginosa are encountered.

Activity of Ceftolozane-Tazobactam Against Gram-Negative Isolates from Australia and New Zealand as part of the PACTS Surveillance 2016-2018

OBJECTIVES

Ceftolozane-tazobactam (C-T) is an anti-pseudomonal cephalosporin combined with a well-described β-lactamase inhibitor. Ceftolozane-tazobactam has enhanced activity against Pseudomonas aeruginosa, and activity against Enterobacterales isolates that produce extended-spectrum β-lactamases (ESBLs) or AmpC cephalosporinases. In this study, we analysed the susceptibility of Gram-negative isolates to C-T and comparators collected in Australia and New Zealand from 2016 to 2018 as part of the Program to Assess Ceftolozane-Tazobactam Susceptibility (PACTS) surveillance.

METHODS

A total of 1693 nonduplicate Enterobacterales and 435 P. aeruginosa isolates were collected prospectively from hospitalized patients in six medical centres in Australia and two in New Zealand. Susceptibilities (S) to C-T and comparators were determined using broth microdilution. EUCAST breakpoints were used. Isolates with multi-drug resistant (MDR), extensively drug resistant (XDR), extended-spectrum β-lactamase non-carbapenem resistant (ESBL, non-CRE) phenotype, and CRE were analysed.

RESULTS

For P. aeruginosa, 97.5% were S to C-T while 89.9% were S to meropenem. According to EUCAST criteria, 86.4% were susceptible-increased exposure to piperacillin-tazobactam. MDR and XDR P. aeruginosa isolates had 76.7% and 65.4% S to C-T, respectively; 34.9% and 19.2% S to meropenem, respectively; and 23.3% and 15.4% were susceptible-increased exposure to piperacillin-tazobactam, respectively. Meropenem (99.8% S), amikacin (99.1% S), and C-T (96.5% S) were the most active against Enterobacterales. Susceptibilities to C-T were 94.3% for ESBL, non-CRE phenotype, and 78.4% for MDR isolates. Only three CRE and five XDR isolates were identified.

CONCLUSIONS

These in vitro data indicate that C-T is a potent antimicrobial with activity against MDR and XDR P. aeruginosa, as well as ESBL, non-CRE phenotype isolates and MDR Enterobacterales.

The plethora of resistance mechanisms in Pseudomonas aeruginosa: transcriptome analysis reveals a potential role of lipopolysaccharide pathway proteins to novel β-lactam/β-lactamase inhibitor combinations

OBJECTIVES

Whole genome and transcriptome analysis of 213 Pseudomonas aeruginosa isolates resistant to antipseudomonal β-lactams collected in 30 countries was performed to evaluate resistance mechanisms against these agents.

METHODS

Isolates were susceptibility tested by reference broth microdilution. Whole genome and transcriptome sequencing were performed, and data were analysed using open-source tools. A statistical analysis of changes in the expression of >5500 genes was compared to the expression of PAO1.

RESULTS

The high-risk clones ST235 and ST111 were the most prevalent among >90 sequence types (STs). Metallo-β-lactamase (MBLs) genes were detected in 40 isolates. AmpC and MexXY were the most common genes overexpressed in approximately 50% of the 173 isolates that did not carry MBLs. Isolates overexpressing pmrA and pmrB, the norspermidine production genes speD2 and speE2, and the operon arnBCADTEF-ugd were noted among strains resistant to ceftolozane-tazobactam and ceftazidime-avibactam, despite the lack of polymyxin resistance often associated to increased expression of these genes. Overexpression of MuxABC-OpmB, OprG, and OprE proteins were associated with resistance to ceftolozane-tazobactam in addition to the usual genes involved in cephalosporin, monobactam, and carbapenem resistance. Statistical analysis identified discrete mutations in ArmZ, OprD, and AmpC that correlated to antipseudomonal β-lactam resistance.

CONCLUSIONS

P. aeruginosa resistance mechanisms are complex. This analysis suggests the role of multiple genes in resistance to antipseudomonal β-lactams, including some not commonly described.

Evaluation of the inoculum effect of new antibiotics against carbapenem-resistant enterobacterales

OBJECTIVES

New antibiotics have been developed to treat multidrug-resistant Enterobacterales. We evaluated the impact of the inoculum size on minimal inhibitory concentrations (MICs) of recently commercialized antibiotics.

METHODS

We focused on 40 clinical carbapenemase-producing Enterobacterales and evaluated the impact of the inoculum size on the MICs to cefiderocol and to new β-lactams/β-lactamase inhibitors (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam, and meropenem-vaborbactam) at usual and high inocula (105 and 107 CFU/mL, respectively).

RESULTS

At usual inoculum, 15% were resistant to cefiderocol (n = 6), 30% to meropenem-vaborbactam (n = 12), 42.5% to ceftazidime-avibactam (n = 17), 55% to imipenem-relebactam (n = 22), and 90% to ceftolozane-tazobactam (n = 36). At higher inoculum, a switch from susceptible to resistant category was observed for 88% (n = 30/34; CI, 71.6-96.2), 75% (n = 3/4; CI, 21.9-98.7), 72% (n = 13/18; CI, 46.4-89.3), 50% (n = 14/28; CI, 31.1-68.9), and 8.7% (n = 2/23; CI, 1.5-29.5) isolates regarding cefiderocol, ceftolozane-tazobactam, imipenem-relebactam, meropenem-vaborbactam, and ceftazidime-avibactam, respectively.

DISCUSSION

Cefiderocol and meropenem-vaborbactam were the most efficient against carbapenemase-producing Enterobacterales at usual inoculum. When increasing inoculum to 107 CFU/mL, all of the molecules were impacted, particularly cefiderocol and imipenem-relebactam, while others, such as ceftazidime-avibactam, remain mildly affected. Our in vitro results deserved to be confirmed in vivo.

Assessing Rates of Co-Resistance and Patient Outcomes in Multidrug-Resistant Pseudomonas aeruginosa

Multidrug-resistant (MDR) Pseudomonas aeruginosa infections are associated with poor patient outcomes due to complex co-resistance patterns. We described common co-resistance patterns, clinical characteristics, and associated outcomes in patients admitted with an MDR P. aeruginosa. This national, multicenter, retrospective cohort study within the Veterans Affairs included adults hospitalized with a MDR P. aeruginosa infection (January 2015-December 2020) per Centers for Disease Control definition. Clinical outcomes were compared among those with differing MDR P. aeruginosa co-resistance: resistant to carbapenems and extended-spectrum cephalosporins and piperacillin-tazobactam (CARB/ESC/PT) versus without CARB/ESC/PT resistance; resistant to carbapenems and extended-spectrum cephalosporins and fluoroquinolone (CARB/ESC/FQ) versus without CARB/ESC/FQ resistance. We included 3,763 hospitalized patients. Co-resistance to CARB/ESC/PT was observed in 42.7%, and to CARB/ESC/FQ in 40.7%. The lowest co-resistance rates were observed with ceftolozane-tazobactam (6.2%, n = 6/97; 12.5%, n = 10/80, respectively) and ceftazidime-avibactam (5.2%, n = 5/97; 12.5%, n = 10/80, respectively). Overall, 14.2% of patients died during hospitalization, 59.7% had an extended length of stay, and 14.9% had reinfection with hospitalization. Outcomes were similar between patients with MDR P. aeruginosa strains with and without co-resistance to CARB/ESC/PT and CARB/ESC/FQ. Among a national cohort of patients hospitalized with MDR P. aeruginosa infections, co-resistance to three classes of standard of care antibiotics, such as carbapenem, extended-spectrum cephalosporins, and piperacillin-tazobactam or fluoroquinolones, exceeded 40% in our study population, posing great concerns for selecting appropriate empirical therapy. Clinical outcomes were poor for all patients, regardless of different co-resistance patterns. New treatment options are needed for hospitalized patients with suspected or confirmed MDR P. aeruginosa infections. IMPORTANCE We studied antibiotic co-resistance patterns in a national group of hospitalized patients with infections due to multidrug-resistant (MDR) Pseudomonas aeruginosa, a type of bacteria that resists treatment to at least three classes of antibiotics. Co-resistance to antibiotic classes most typically used for treatment was common, which makes selecting appropriate antibiotics to successfully treat the infections difficult. Outcomes, including death, were poor for all patients in our study, regardless of the different patterns of co-resistance to common antibiotic classes. New antibiotics are needed to help treat hospitalized patients with MDR P. aeruginosa infections.

Role of Enzymatic Activity in the Biological Cost Associated with the Production of AmpC β-Lactamases in Pseudomonas aeruginosa

In the current scenario of growing antibiotic resistance, understanding the interplay between resistance mechanisms and biological costs is crucial for designing therapeutic strategies. In this regard, intrinsic AmpC β-lactamase hyperproduction is probably the most important resistance mechanism of Pseudomonas aeruginosa, proven to entail important biological burdens that attenuate virulence mostly under peptidoglycan recycling alterations. P. aeruginosa can acquire resistance to new β-lactam-β-lactamase inhibitor combinations (ceftazidime-avibactam and ceftolozane-tazobactam) through mutations affecting ampC and its regulatory genes, but the impact of these mutations on the associated biological cost and the role that β-lactamase activity plays per se in contributing to the above-mentioned virulence attenuation are unknown. The same questions remain unsolved for plasmid-encoded AmpC-type β-lactamases such as FOX enzymes, some of which also provide resistance to new β-lactam-β-lactamase inhibitor combinations. Here, we assessed from different perspectives the effects of changes in the active center and, thus, in the hydrolytic spectrum resistance to inhibitors of AmpC-type β-lactamases on the fitness and virulence of P. aeruginosa, using site-directed mutagenesis; the previously described AmpC variants T96I, G183D, and ΔG229-E247; and, finally, blaFOX-4 versus blaFOX-8. Our results indicate the essential role of AmpC activity per se in causing the reported full virulence attenuation (in terms of growth, motility, cytotoxicity, and Galleria mellonella larvae killing), although the biological cost of the above-mentioned AmpC-type variants was similar to that of the wild-type enzymes. This suggests that there is not an important biological burden that may limit the selection/spread of these variants, which could progressively compromise the future effectiveness of the above-mentioned drug combinations. IMPORTANCE The growing antibiotic resistance of the top nosocomial pathogen Pseudomonas aeruginosa pushes research to explore new therapeutic strategies, for which the resistance-versus-virulence balance is a promising source of targets. While resistance often entails significant biological costs, little is known about the bases of the virulence attenuations associated with a resistance mechanism as extraordinarily relevant as β-lactamase production. We demonstrate that besides potential energy and cell wall alterations, the enzymatic activity of the P. aeruginosa cephalosporinase AmpC is essential for causing the full attenuation associated with its hyperproduction by affecting different features related to pathogenesis, a fact exploitable from the antivirulence perspective. Less encouraging, we also show that the production of different chromosomal/plasmid-encoded AmpC derivatives conferring resistance to some of the newest antibiotic combinations causes no significantly increased biological burdens, which suggests a free way for the selection/spread of these types of variants, potentially compromising the future effectiveness of these antipseudomonal therapies.

Antimicrobial Activity of Ceftolozane-Tazobactam, Ceftazidime-Avibactam, and Cefiderocol against Multidrug-Resistant Pseudomonas aeruginosa Recovered at a German University Hospital

Multidrug-resistant (MDR) Pseudomonas aeruginosa increasingly causes health care-associated infections. In this study, we determined the activity of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against 223 MDR P. aeruginosa clinical isolates recovered from 2013 to 2017 at the University Hospital Frankfurt by using MIC test strips. Furthermore, we evaluated the presence of genes encoding major β-lactamases, such as VIM, IMP, NDM, GIM, SPM, and KPC; the extended spectrum β-lactamase (ESBL)-carbapenemase GES; and the virulence-associated traits ExoS and ExoU, as in particular ExoU is thought to be associated with poor clinical outcome. For MDR P. aeruginosa isolates, the MIC50/MIC90 values of ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol were 8/>256 mg/L, 16/>256 mg/L, and 0.25/1 mg/L, respectively. Cefiderocol showed the highest susceptibility rate (97.3%) followed by ceftazidime-avibactam (48.4%) and ceftolozane-tazobactam (46.6%). In 81 (36.3%) isolates, carbapenemase gene blaVIM was detected, and in 5 (2.2%) isolates, blaGES was detected (with a positive association of exoU and blaVIM). More than half of the isolates belong to the so-called international P. aeruginosa "high-risk" clones, with sequence type 235 (ST235) (24.7%) being the most prevalent. This study underlines that ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol are important options for the treatment of infections due to MDR P. aeruginosa, with cefiderocol currently being the most active available antipseudomonal β-lactam agent. According to our clinical experience, the outcome of cefiderocol therapy (8 patients) was favorable especially in cases of MDR P. aeruginosa-associated complicated urinary tract infections. IMPORTANCE After testing ceftolozane-tazobactam, ceftazidime-avibactam, and cefiderocol against a collection of 233 multidrug-resistant (MDR) Pseudomonas aeruginosa, we showed that cefiderocol is the most active antipseudomonal β-lactam agent (susceptibility rates were 46.6%, 48.4%, and 97.4%, respectively). The most prevalent one was sequence type 235 (ST235) (24.7%), followed by ST244, ST175, and ST233, with all belonging to the top 10 P. aeruginosa high-risk clones with worldwide distribution. Our data indicate that during surveillance studies special attention should be paid to the MDR and highly virulent VIM- and ExoU-producing variant of ST235. Furthermore, in the case of infections caused by carbapenemase-producing MDR P. aeruginosa, cefiderocol is the preferred treatment option, while outcomes of complicated urinary tract infections and hospital-acquired pneumonia with cefiderocol were favorable.

Treatment of multidrug-resistant Pseudomonas aeruginosa bacteremia using ceftolozane-tazobactam-based or colistin-based antibiotic regimens: A multicenter retrospective study

BACKGROUND

Ceftolozane-tazobactam is an emerging ‎treatment for severe infections caused by multidrug-resistant (MDR) Pseudomonas ‎aeruginosa. However, limited ‎data support its use in bacteremia treatment. This study aimed to assess the effectiveness of the treatment of MDR P. aeruginosa bacteremia using ceftolozane-‎tazobactam-based or colistin-based regimens. ‎ PATIENTS AND METHODS: This retrospective, cohort, multicentre study included adult patients with ‎MDR P. aeruginosa bacteremia treated with either ceftolozane-tazobactam or ‎colistin, between September 2018 and August 2021, at four hospitals in Saudi ‎Arabia. The primary endpoint was the 30-day risk-adjusted mortality. Secondary endpoints included the 14-day risk of mortality, bacterial eradication, and clinical ‎success. Cox proportional hazards ‎regression and relative risk estimation were used for analysis, as appropriate. ‎ RESULTS: In total, 46 patients were included; 17 patients received ceftolozane-‎tazobactam-based regimen, and 29 received a colistin-based regimen. There was no association with the use of ‎ceftolozane-tazobactam compared to colistin and the 30-day risk-adjusted mortality ‎‎(hazard ratio [HR] ‎0.58, 95% confidence interval [CI] 0.16-2.13, P = 0.42). Also, the ‎‎14-day risk of mortality and bacterial eradication were not different between the ‎ceftolozane-tazobactam and colistin regimens, HR 2.1, 95% CI 0.42-10.48; P = 0.36; and ‎relative risk (RR) 0.65; 95% CI 0.28-1.52; P = 0.30; respectively. On the other hand, ‎ceftolozane-tazobactam use was associated with higher clinical success than colistin ‎‎(RR 1.84, 95% CI 1.11-3.06: P = 0.021).‎ CONCLUSION: The risk of mortality of MDR P.aeruginosa bacteremia was ‎similar when treated with ceftolozane-tazobactam-based or colistin-based antimicrobial regimens. A higher clinical success was observed with the ceftolozane-‎tazobactam-based regimen compared to the colistin-based regimen. ‎.

Activity of ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, cefiderocol and comparators against Gram-negative organisms causing bloodstream infections in Northern Italy (2019-2021): emergence of complex resistance phenotypes

Herein we assessed the frequency of Gram-negative organisms causing bloodstream infections and activity spectrum of ceftolozane-tazobactam (CTZ), ceftazidime-avibactam (CZA), meropenem-vaborbactam (MEV), cefiderocol (CFDC) and comparators. Overall, 1605 Gram-negative isolates were consecutively collected during 2019-2021. Enterobacterales represented more than 75% and exhibited >90% susceptibility to CZA (97%), amikacin (91.8%) and meropenem (90.6%). ESBL-producing Enterobacterales isolates showed high rates of susceptibility towards CZA (100%), carbapenems (89.1-100%) and CTZ (84.9-95.1%). MEV displayed the highest activity against KPC-producing Enterobacterales (MIC50/90, 0.75/4 mg/L; 92.9% susceptible) followed by CZA (MIC50/90, ≤2/>8 mg/L; 89.3% susceptible), CFDC (MIC50/90, 0.25/4 mg/L, 87.5% susceptible) and colistin (MIC50/90, ≤2/4 mg/L, 83.9% susceptible). High proportions of P. aeruginosa isolates were susceptible to colistin (97.8%), CZA (97.2%), CTZ (96.1%) and amikacin (94.5%). CFDC showed potent activity against Acinetobacter baumannii (MIC50/90, 0.5/1 mg/L; 97.2% susceptible), multi-drug resistant P. aeruginosa (MIC50/90, 0.25/1 mg/L; 96% susceptible), and Stenotrophomonas maltophilia (MIC50/90, 0.12/0.25 mg/L; 100% susceptible).

Genomic Surveillance of Clinical Pseudomonas aeruginosa Isolates Reveals an Additive Effect of Carbapenemase Production on Carbapenem Resistance

Carbapenem resistance in Pseudomonas aeruginosa is increasing globally, and surveillance to define the mechanisms of such resistance in low- and middle-income countries is limited. This study establishes the genotypic mechanisms of β-lactam resistance by whole-genome sequencing (WGS) in 142 P. aeruginosa clinical isolates recovered from three hospitals in Islamabad and Rawalpindi, Pakistan between 2016 and 2017. Isolates were subjected to antimicrobial susceptibility testing (AST) by Kirby-Bauer disk diffusion, and their genomes were assembled from Illumina sequencing data. β-lactam resistance was high, with 46% of isolates resistant to piperacillin-tazobactam, 42% to cefepime, 48% to ceftolozane-tazobactam, and 65% to at least one carbapenem. Twenty-two percent of isolates were resistant to all β-lactams tested. WGS revealed that carbapenem resistance was associated with the acquisition of metallo-β-lactamases (MBLs) or extended-spectrum β-lactamases (ESBLs) in the blaGES, blaVIM, and blaNDM families, and mutations in the porin gene oprD. These resistance determinants were found in globally distributed lineages, including ST235 and ST664, as well as multiple novel STs which have been described in a separate investigation. Analysis of AST results revealed that acquisition of MBLs/ESBLs on top of porin mutations had an additive effect on imipenem resistance, suggesting that there is a selective benefit for clinical isolates to encode multiple resistance determinants to the same drugs. The strong association of these resistance determinants with phylogenetic background displays the utility of WGS for monitoring carbapenem resistance in P. aeruginosa, while the presence of these determinants throughout the phylogenetic tree shows that knowledge of the local epidemiology is crucial for guiding potential treatment of multidrug-resistant P. aeruginosa infections. IMPORTANCE Pseudomonas aeruginosa is associated with serious infections, and treatment can be challenging. Because of this, carbapenems and β-lactam/β-lactamase inhibitor combinations have become critical tools in treating multidrug-resistant (MDR) P. aeruginosa infections, but increasing resistance threatens their efficacy. Here, we used WGS to study the genotypic and phylogenomic patterns of 142 P. aeruginosa isolates from the Potohar region of Pakistan. We sequenced both MDR and antimicrobial susceptible isolates and found that while genotypic and phenotypic patterns of antibiotic resistance correlated with phylogenomic background, populations of MDR P. aeruginosa were found in all major phylogroups. We also found that isolates possessing multiple resistance mechanisms had significantly higher levels of imipenem resistance compared to the isolates with a single resistance mechanism. This study demonstrates the utility of WGS for monitoring patterns of antibiotic resistance in P. aeruginosa and potentially guiding treatment choices based on the local spread of β-lactamase genes.

The effects of antibiotic cycling and mixing on acquisition of antibiotic resistant bacteria in the ICU: A post-hoc individual patient analysis of a prospective cluster-randomized crossover study

Background

Repeated rotation of empiric antibiotic treatment strategies is hypothesized to reduce antibiotic resistance. Clinical rotation studies failed to change unit-wide prevalence of antibiotic resistant bacteria (ARB) carriage, including an international cluster-randomized crossover study. Unit-wide effects may differ from individual effects due to “ecological fallacy”. This post-hoc analysis of a cluster-randomized crossover study assesses differences between cycling and mixing rotation strategies in acquisition of carriage with Gram-negative ARB in individual patients.

Methods

This was a controlled cluster-randomized crossover study in 7 ICUs in 5 European countries. Clinical cultures taken as routine care were used for endpoint assessment. Patients with a first negative culture and at least one culture collected in total were included. Community acquisitions (2 days of admission or less) were excluded. Primary outcome was ICU-acquisition of Enterobacterales species with reduced susceptibility to: third- or fourth generation cephalosporins or piperacillin-tazobactam, and Acinetobacter species and Pseudomonas aeruginosa with reduced susceptibility for piperacillin-tazobactam or carbapenems. Cycling (altering first-line empiric therapy for Gram-negative bacteria, every other 6-weeks), to mixing (changing antibiotic type every empiric antibiotic course). Rotated antibiotics were third- or fourth generation cephalosporins, piperacillin-tazobactam and carbapenems.

Results

For this analysis 1,613 admissions were eligible (855 and 758 during cycling and mixing, respectively), with 16,437 microbiological cultures obtained. Incidences of acquisition with ARB during ICU-stay were 7.3% (n = 62) and 5.1% (n = 39) during cycling and mixing, respectively (p-value 0.13), after a mean of 17.7 (median 15) and 20.8 (median 13) days. Adjusted odds ratio for acquisition of ARB carriage during mixing was 0.62 (95% CI 0.38 to 1.00). Acquired carriage with ARB were Enterobacterales species (n = 61), Pseudomonas aeruginosa (n = 38) and Acinetobacter species (n = 20), with no statistically significant differences between interventions.

Conclusions

There was no statistically significant difference in individual patients’ risk of acquiring carriage with Gram-negative ARB during cycling and mixing. These findings substantiate the absence of difference between cycling and mixing on the epidemiology of Gram-negative ARB in ICU.

Trial registration

This trial is registered with ClinicalTrials.gov, registered 10 January 2011, NCT01293071.

Ceftolozane-tazobactam in nosocomial pneumonia

Ceftolozane is a potent antimicrobial against Pseudomonas aeruginosa, including carbapenem-resistant and multidrug-resistant strains, and is also active against Enterobacteriaceae. It MIC (minimal inhibitory concentration) and MPC (mutant preventive concentration) are close together, allowing to avoid the mutant selection window specifically in the treatment of Pseudomonas aeruginosa infection. The molecule is time-dependent and stable when reconstituted at room temperature, facilitating safe and effective dosage optimization in frail and critically ill patients. It has been shown to be non-inferior to meropenem in the treatment of nosocomial infection in the ASPECT-NP study but superior in post-hoc studies in the subgroup of patients with ventilator-associated pneumonia, without the emergence of resistance during treatment. It is FDA approved at a dose of 3 g every 8 hours in the treatment of nosocomial pneumonia (HABP/VABP) in adults.

In vitro activity of cefiderocol against Gram-negative bacterial pathogens in Germany

OBJECTIVES

Widespread antimicrobial resistance in Gram-negative bacteria (GNB), particularly carbapenem resistance, represents a major clinical challenge. Cefiderocol is a novel siderophore cephalosporin active against all carbapenemase classes.

METHODS

We evaluated the in vitro activity of cefiderocol and other antibacterial agents (ceftazidime/avibactam, ceftolozane/tazobactam, colistin and meropenem) against GNB isolates collected in Germany (2013-2018) as part of two multinational studies. Antimicrobial susceptibility testing was performed by broth microdilution. Minimum inhibitory concentrations were interpreted according to EUCAST breakpoints.

RESULTS

Cefiderocol had high activity against GNB isolates (N = 2298), encompassing both Enterobacterales (n = 1562) and non-fermenter species (n = 736), and maintained high activity against carbapenem-resistant strains (n = 211). The activity of cefiderocol against Enterobacterales was equivalent to that of ceftazidime/avibactam and colistin, while ceftolozane/tazobactam was somewhat less active. Against non-fermenter species, cefiderocol displayed equivalent activity to colistin; both of these agents were more active than ceftazidime/avibactam and ceftolozane/tazobactam. Colistin had similar activity to cefiderocol against the majority of species. These patterns of activity were echoed in carbapenem-resistant isolates. The high activity of cefiderocol was independent of infection site, whereas other antibacterial agents demonstrated slightly lower activity against isolates causing pneumonia compared with those from other key infection sites.

CONCLUSION

Cefiderocol exhibited consistently high in vitro activity against a variety of GNB isolates collected in Germany, including resistant phenotypes, across multiple infection sites. These data suggest that cefiderocol is an effective choice of antibacterial agent in patients with GNB infection, regardless of species and resistance phenotype to other agents.

Evaluation of MicroScan WalkAway for Determination of Ceftazidime-Avibactam and Ceftolozane-Tazobactam Susceptibility in Carbapenem-Resistant Gram-Negative Bacilli

We evaluated the performance of ceftazidime-avibactam and ceftolozane-tazobactam MicroScan Neg multidrug-resistant MIC 1 (NMR1) panel for clinical carbapenem-nonsusceptible Gram-negative bacilli isolates. We evaluated 212 clinically significant carbapenem-nonsusceptible Gram-negative bacilli (139 Pseudomonas aeruginosa and 73 KPC-producing Enterobacterales) from 71 Brazilian hospitals (2013 to 2020). Ceftazidime-avibactam and ceftolozane-tazobactam MICs from the panel were compared with a broth microdilution (BMD) test as the reference method. Essential agreement (EA) and categorical agreement (CA) were assessed. For P. aeruginosa, antimicrobial susceptibility testing error rates were calculated using the error-rate bound method. Discrepancies were initially observed with 11 isolates; 4 resolved after retesting, 2 in favor of the NMR1 and 2 in favor of the BMD method. The ceftazidime-avibactam EA (overall and evaluable) was 100% for P. aeruginosa and Enterobacterales. The CA was 100% for Enterobacterales and 98.6% for P. aeruginosa. The ceftolozane-tazobactam EA was 98.6% and 100% (overall and evaluable, respectively), and the CA was 96.4% for P. aeruginosa. For ceftazidime/avibactam, no very major error (VME) was found, and the major error (ME) rate was 4.2% (2/48). For ceftolozane-tazobactam and P. aeruginosa, using the CLSI breakpoints, the minor error (mE) was 11.4%, and no VME or ME was found. While using EUCAST breakpoints, the VME was 11.4% with no ME. The mE becomes ME or VME in the absence of the intermediate category. All categorical errors were also within 1 log of MIC variation, and the adjusted error rate for CLSI/EUCAST was 0% (0/212). The NMR1 panel is an option to test ceftazidime-avibactam for KPC-producing Enterobacterales and carbapenem-nonsusceptible P. aeruginosa. When a MIC of 4 mg/liter for ceftolozane-tazobactam is obtained using this method, an alert could be created, and the results could be confirmed by an alternative method.

Advances in novel antibiotics to treat multidrug-resistant gram-negative bacterial infections

Antimicrobial resistance is a growing threat to public health and an increasingly common problem for acute care physicians to confront. Several novel antibiotics have been approved in the past decade to combat these infections; however, physicians may be unfamiliar with how to appropriately utilize them. The purpose of this review is to evaluate novel antibiotics active against resistant gram-negative bacteria and highlight clinical information regarding their use in the acute care setting. This review focuses on novel antibiotics useful in the treatment of infections caused by resistant gram-negative organisms that may be seen in the acute care setting. These novel antibiotics include ceftolozane/tazobactam, ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilistatin/relebactam, cefiderocol, plazomicin, eravacycline, and omadacycline. Acute care physicians should be familiar with these novel antibiotics so they can utilize them appropriately.

The role of tazobactam-based combinations for the management of infections due to extended-spectrum β-lactamase-producing Enterobacterales: Insights from the Society of Infectious Diseases Pharmacists

Extended-spectrum β-lactamase (ESBL)-producing Enterobacterales are a global threat to public health due to their antimicrobial resistance profile and, consequently, their limited available treatment options. Tazobactam is a sulfone β-lactamase inhibitor with in vitro inhibitory activity against common ESBLs in Enterobacterales, including CTX-M. However, the role of tazobactam-based combinations in treating infections caused by ESBL-producing Enterobacterales remains unclear. In the United States, two tazobactam-based combinations are available, piperacillin-tazobactam and ceftolozane-tazobactam. We evaluated and compared the roles of tazobactam-based combinations against ESBL-producing organisms with emphasis on pharmacokinetic/pharmacodynamic exposures in relation to MIC distributions and established breakpoints, clinical outcomes data specific to infection site, and considerations for downstream effects with these agents regarding antimicrobial resistance development. While limited data with ceftolozane-tazobactam are encouraging for its potential role in infections due to ESBL-producing Enterobacterales, further evidence is needed to determine its place in therapy. Conversely, currently available microbiologic, pharmacokinetic, pharmacodynamic, and clinical data do not suggest a role for piperacillin-tazobactam, and we caution clinicians against its usage for these infections.

Ceftolozane-tazobactam activity against clinical isolates of Pseudomonas aeruginosa from ICU patients with pneumonia: United States, 2015-2018

OBJECTIVES

To report on the activity of ceftolozane-tazobactam and comparators against Pseudomonas aeruginosa isolates collected from hospitalized patients with pneumonia in US intensive care units (ICUs) between 2015 and 2018. Activity against all P. aeruginosa and common resistant phenotypes are described to better inform decision-making and support antimicrobial stewardship efforts.

METHODS

In total, 781 P. aeruginosa isolates were collected from 28 US hospitals. These isolates were tested for susceptibility to ceftolozane-tazobactam and comparators by Clinical and Laboratory Standards Institute (CLSI) broth microdilution methodology using CLSI (2020) breakpoints. Phenotypes analysed included piperacillin-tazobactam-non-susceptible (NS), cefepime-NS, ceftazidime-NS, meropenem-NS and difficult-to-treat resistance (DTR).

RESULTS

Ceftolozane-tazobactam was the most potent agent tested (minimum inhibitory concentration to inhibit 50% and 90% of isolates of 0.5 and 2 mg/L, respectively, inhibiting 97.2% at the susceptible breakpoint of ≤4 mg/L). Traditional first-line antipseudomonal β-lactam antibiotics (piperacillin-tazobactam, cefepime and ceftazidime) demonstrated <33% susceptibility when P. aeruginosa was NS to one or more agent. Although escalation of therapy to meropenem is commonly employed clinically, meropenem susceptibility ranged from 33.6% to 44.9% if P. aeruginosa was NS to any traditional first-line antipseudomonal β-lactam agent. Conversely, ceftolozane-tazobactam remained active against isolates that were NS to other agents, inhibiting 88.4% of isolates NS to piperacillin-tazobactam, 85.0% of isolates NS to cefepime and ceftazidime, and 90.3% of isolates NS to meropenem. Ceftolozane-tazobactam also maintained activity against 73.0% of DTR isolates.

CONCLUSIONS

Ceftolozane-tazobactam maintained high activity against P. aeruginosa isolated from hospitalized patients with pneumonia in US ICUs, and had the greatest activity against isolates NS to one or more antipseudomonal β-lactams and DTR isolates.

Activity of ceftolozane/tazobactam against Gram-negative isolates from patients with lower respiratory tract infections - SMART United States 2018-2019

BACKGROUND

Ceftolozane/tazobactam (C/T) is approved in 70 countries, including the United States, for the treatment of patients with hospital-acquired and ventilator-associated bacterial pneumonia caused by susceptible Gram-negative pathogens. C/T is of particular importance as an agent for the treatment of multidrug-resistant (MDR) Pseudomonas aeruginosa infections. The current study summarizes 2018-2019 data from the United States on lower respiratory tract isolates of Gram-negative bacilli from the SMART global surveillance program. The CLSI reference broth microdilution method was used to determine in vitro susceptibility of C/T and comparators against isolates of P. aeruginosa and Enterobacterales.

RESULTS

C/T inhibited 96.0% of P. aeruginosa (n = 1237) at its susceptible MIC breakpoint (≤4 μg/ml), including > 85% of meropenem-nonsusceptible and piperacillin/tazobactam (P/T)-nonsusceptible isolates and 76.2% of MDR isolates. Comparator agents demonstrated lower activity than C/T against P. aeruginosa: meropenem (74.8% susceptible), cefepime (79.2%), ceftazidime (78.5%), P/T (74.4%), and levofloxacin (63.1%). C/T was equally active against ICU (96.0% susceptible) and non-ICU (96.7%) isolates of P. aeruginosa. C/T inhibited 91.8% of Enterobacterales (n = 1938) at its susceptible MIC breakpoint (≤2 μg/ml); 89.5% of isolates were susceptible to cefepime and 88.0% susceptible to P/T. 67.1 and 86.5% of extended-spectrum β-lactamase (ESBL) screen-positive isolates of Klebsiella pneumoniae (n = 85) and Escherichia coli (n = 74) and 49.6% of MDR Enterobacterales were susceptible to C/T. C/T was equally active against ICU (91.3% susceptible) and non-ICU (92.6%) Enterobacterales isolates.

CONCLUSION

Data from the current study support the use of C/T as an important treatment option for lower respiratory tract infections including those caused by MDR P. aeruginosa.

Piperacillin/tazobactam resistance in a clinical isolate of Escherichia coli due to IS26-mediated amplification of blaTEM-1B

A phenotype of Escherichia coli and Klebsiella pneumoniae, resistant to piperacillin/tazobactam (TZP) but susceptible to carbapenems and 3rd generation cephalosporins, has emerged. The resistance mechanism associated with this phenotype has been identified as hyperproduction of the β-lactamase TEM. However, the mechanism of hyperproduction due to gene amplification is not well understood. Here, we report a mechanism of gene amplification due to a translocatable unit (TU) excising from an IS26-flanked pseudo-compound transposon, PTn6762, which harbours blaTEM-1B. The TU re-inserts into the chromosome adjacent to IS26 and forms a tandem array of TUs, which increases the copy number of blaTEM-1B, leading to TEM-1B hyperproduction and TZP resistance. Despite a significant increase in blaTEM-1B copy number, the TZP-resistant isolate does not incur a fitness cost compared to the TZP-susceptible ancestor. This mechanism of amplification of blaTEM-1B is an important consideration when using genomic data to predict susceptibility to TZP.

Activity of ceftolozane-tazobactam against Gram-negative pathogens isolated from lower respiratory tract infections in the Asia-Pacific region: SMART 2015-2016

The aim of this study was to investigate the susceptibility of respiratory Gram-negative bacteria to ceftolozane/tazobactam and other antibiotics in the Asia-Pacific region during 2015-2016. MICs were determined using the CLSI standard broth microdilution method and interpreted accordingly. Pseudomonas aeruginosa (1574 isolates), Klebsiella pneumoniae (1226), Acinetobacter baumannii (627) and Escherichia coli (476) accounted for 73.1% of 5342 Gram-negative respiratory pathogens. Susceptibility to ceftolozane/tazobactam of individual Enterobacteriaceae was >80%, except for Enterobacter cloacae (76.6%). Ceftolozane/tazobactam inhibited 81.9% of K. pneumoniae and 91.9% of E. coli, with respective MIC₅₀/MIC₉₀ values of 0.5/>32 and 0.25/2 mg/L. For carbapenem-susceptible, ESBL-producing K. pneumoniae and E. coli, susceptibility was 65.5% and 93.3%, respectively, and respective MIC₅₀/MIC₉₀ values were 2/>32 and 0.5/2 mg/L. Bla_{CTX-M-1 group} was most prevalent in selected ESBL-producing K. pneumoniae (40 of 54 isolates) and E. coli (15 of 22 isolates), with ceftolozane/tazobactam susceptibility rates of 50% and 80%, respectively. Bla_SHV-ESBL was the second most prevalent, and ceftolozane/tazobactam inhibited 20% of 20 K. pneumoniae isolates with bla_SHV-ESBL. The only effective antibiotics for carbapenem-non-susceptible K. pneumoniae (111 isolates) and E. coli (24 isolates) were amikacin and colistin. Ceftolozane/tazobactam was effective against almost all tested P. aeruginosa and carbapenem-non-susceptible strains, with susceptibility of 92.3% and 72.8%, respectively; the respective MIC₅₀/MIC₉₀ values were 1/4 and 2/>32 mg/L. The high susceptibility of ceftolozane/tazobactam remained in different age groups, patient locations, recovery times and countries, except Vietnam. In conclusion, ceftolozane/tazobactam was effective against most respiratory Gram-negative pathogens in the Asia-Pacific region; however, the emergence of carbapenem resistance mandates ongoing surveillance.

In Vitro Activities of β-Lactam-β-Lactamase Inhibitor Antimicrobial Agents against Cystic Fibrosis Respiratory Pathogens

We tested the in vitro activities of ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, piperacillin-tazobactam, and 11 other antimicrobial agents against 420 Burkholderia, Achromobacter, Stenotrophomonas, and Pandoraea strains, 89% of which were cultured from respiratory specimens from persons with cystic fibrosis. Among the β-lactam-β-lactamase inhibitor agents, meropenem-vaborbactam had the greatest activity against Burkholderia and Achromobacter, including multidrug-resistant and extensively-drug-resistant strains. None of the newer β-lactam-β-lactamase combination drugs showed increased activity compared to that of the older agents against Stenotrophomonas maltophilia or Pandoraea spp.

Antimicrobial activity of ceftolozane/tazobactam tested against contemporary (2015-2017) Pseudomonas aeruginosa isolates from a global surveillance programme

OBJECTIVES

Ceftolozane/tazobactam (C-T) is an antimicrobial combination of an antipseudomonal cephalosporin and a β-lactamase inhibitor. C-T has been approved in >60 countries for complicated urinary tract infections, acute pyelonephritis, complicated intra-abdominal infections in combination with metronidazole, and was recently approved for hospital-acquired bacterial pneumonia. In this study, data for Pseudomonas aeruginosa isolates consecutively collected from various infection types in hospitalised patients from 2015 to 2017 were analysed.

METHODS

A total of 6836 P. aeruginosa isolates were collected from 104 hospitals in four continents and were tested for susceptibility to C-T by CLSI broth microdilution methodology at JMI Laboratories using CLSI (2018) breakpoints. Other agents tested included amikacin, ceftazidime (CAZ), colistin (COL), levofloxacin (LVX), meropenem (MEM) and piperacillin/tazobactam (TZP). Resistance phenotypes analysed included CAZ-non-susceptible (CAZ-NS), COL-NS, MEM-NS, LVX-NS, TZP-NS and β-lactam-NS. Multidrug resistance (MDR) was defined as NS to ≥1 drug in ≥3 drug classes, and extensively drug-resistant (XDR) was defined as NS to ≥1 agent in all but 2 or fewer antimicrobial classes.

RESULTS

The most common infection from which P. aeruginosa was isolated was pneumonia (51.6%), followed by skin and skin-structure infection (22.2%) and bloodstream infection (15.3%). Percentage susceptibility to C-T varied by region: 98.2% in North America; 94.8% in Asia-Pacific; 90.8% in Latin America; and 89.1% in Europe.

CONCLUSION

C-T had potent activity against P. aeruginosa isolated from patients in hospitals in four continents. C-T was more active than all comparators, except COL, and maintained activity against MDR and XDR isolates and isolates NS to all four tested β-lactams. C-T was active against 13/16 COL-NS isolates.

In vitro activity of ceftolozane-tazobactam and ceftazidime-avibactam against clinical isolates of meropenem-non-susceptible Pseudomonas aeruginosa: A two-centre study

OBJECTIVES

This study aimed to compare the activity of ceftazidime-avibactam (C/A), ceftolozane-tazobactam (C/T) and three anti-pseudomonal β-lactams (piperacillin-tazobactam, ceftazidime and cefepime) against a collection of meropenem-non-susceptible Pseudomonas aeruginosa (P. aeruginosa) clinical isolates recovered from two centres in Turkey.

METHODS

A total of 102 unique patient isolates of meropenem-non-susceptible P. aeruginosa were included in the study. MICs of antimicrobials were determined by the gradient diffusion method.

RESULTS

Overall susceptibility rates for C/A and C/T were 83.3% and 82.4%, respectively. Both C/A and C/T had better activity than any one of the three anti-pseudomonal β-lactams. According to the MIC₅₀ values, C/T was the most potent agent against isolates. Although the susceptibility rates of isolates to C/T and C/A were similar, C/T (MIC₅₀, 1 μg/mL) was four-fold more potent than C/A (MIC₅₀, 4 μg/mL). The MIC₅₀ values of C/A and C/T for the isolates that were non-susceptible to three β-lactams were significantly higher than those for isolates that were non-susceptible to zero, one or two β-lactams. Also, the C/A MIC₅₀ value for the isolates that were non-susceptible to two β-lactams was higher than that for isolates which were non-susceptible to one β-lactam.

CONCLUSIONS

C/A and C/T showed good activity against meropenem-non-susceptible P. aeruginosa isolates. However, resistance to these agents was not uncommon among these isolates. The overall β-lactam susceptibility profile of isolates seems to have an effect on the probability of susceptibility to C/A and C/T. Antimicrobial susceptibility testing should be performed for C/A and C/T if these agents are considered for treatment of infections caused by meropenem-non-susceptible P. aeruginosa.

Results from the China Antimicrobial Surveillance Network (CHINET) in 2017 of the In Vitro Activities of Ceftazidime-Avibactam and Ceftolozane-Tazobactam against Clinical Isolates of Enterobacteriaceae and Pseudomonas aeruginosa

The in vitro activities of ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C-T), and comparators were determined for 1,774 isolates of Enterobacteriaceae and 524 isolates of Pseudomonas aeruginosa collected by 30 medical centers from the China Antimicrobial Surveillance Network (CHINET) in 2017. Antimicrobial susceptibility testing was performed by the CLSI broth microdilution method, and blaKPC and blaNDM were detected by PCR for all carbapenem-resistant Enterobacteriaceae (CRE). Ceftazidime-avibactam demonstrated potent activity against almost all Enterobacteriaceae (94.6% susceptibility; MIC50, ≤0.25 mg/liter; MIC90, ≤0.25 to >32 mg/liter) and good activity against P. aeruginosa (86.5% susceptibility; MIC50/90, 2/16 mg/liter). Among the CRE, 50.8% (189/372 isolates) were positive for blaKPC-2, which mainly existed in ceftazidime-avibactam-susceptible Klebsiella pneumoniae isolates (92.1%, 174/189). Among the CRE, 17.7% (66/372 isolates) were positive for blaNDM, which mainly existed in strains resistant to ceftazidime-avibactam (71.7%, 66/92). Ceftolozane-tazobactam showed good in vitro activity against Escherichia coli and Proteus mirabilis (MIC50/90, ≤0.5/2 mg/liter; 90.5 and 93.8% susceptibility, respectively), and the rates of susceptibility of K. pneumoniae (MIC50/90, 2/>64 mg/liter) and P. aeruginosa (MIC50/90, 1/8 mg/liter) were 52.7% and 88.5%, respectively. Among the CRE strains, 28.6% of E. coli isolates and 85% of K. pneumoniae isolates were still susceptible to ceftazidime-avibactam, but only 7.1% and 1.9% of them, respectively, were susceptible to ceftolozane-tazobactam. The rates of susceptibility of the carbapenem-resistant P. aeruginosa isolates to ceftazidime-avibactam (65.7%) and ceftolozane-tazobactam (68%) were similar. Overall, both ceftazidime-avibactam and ceftolozane-tazobactam were highly active against clinical isolates of Enterobacteriaceae and P. aeruginosa recently collected across China, and ceftazidime-avibactam showed activity superior to that of ceftolozane-tazobactam against Enterobacteriaceae, whereas ceftolozane-tazobactam showed a better effect against P. aeruginosa.

In vitro activities of cefiderocol, ceftolozane/tazobactam, ceftazidime/avibactam and other comparative drugs against imipenem-resistant Pseudomonas aeruginosa and Acinetobacter baumannii, and Stenotrophomonas maltophilia, all associated with bloodstream infections in Taiwan

Objectives

We investigated the in vitro activities of cefiderocol, ceftazidime/avibactam, ceftolozane/tazobactam and other related drugs against imipenem-resistant Pseudomonas aeruginosa, imipenem-resistant Acinetobacter baumannii and Stenotrophomonas maltophilia isolates.

Methods

Non-duplicated bacteraemia isolates (n = 300) of imipenem-resistant P. aeruginosa (n = 100), imipenem-resistant A. baumannii (n = 100) and S. maltophilia (n = 100) were evaluated. Imipenem-resistant P. aeruginosa and imipenem-resistant A. baumannii isolates were defined as isolates exhibiting imipenem MIC ≥8 mg/L, as determined using the VITEK 2 system. The MICs of 11 other antimicrobial agents for the isolates were determined by the broth microdilution method. Iron-depleted CAMHB was used to determine the MICs of cefiderocol.

Results

The rates of colistin resistance of imipenem-resistant P. aeruginosa and imipenem-resistant A. baumannii were 5% and 10%, respectively. The MIC90 values of cefiderocol, ceftolozane/tazobactam, ceftazidime/avibactam, tigecycline and colistin were as follows: imipenem-resistant P. aeruginosa: 1, 4, 16, >4 and 2 mg/L; imipenem-resistant A. baumannii: 8, >64, >64, 4 and 2 mg/L; and S. maltophilia: 0.25, >64, >64, 2 and >8 mg/L, respectively. For imipenem-resistant A. baumannii isolates, the MICs of cefiderocol, ceftolozane/tazobactam and ceftazidime/avibactam were ≤4 mg/L for 88%, 8% and 1% of the isolates, respectively. Cefiderocol MICs were ≤4 mg/L for the five colistin-resistant imipenem-resistant P. aeruginosa isolates and 70% of the 10 colistin-resistant imipenem-resistant A. baumannii isolates.

Conclusions

Cefiderocol exhibited more potent in vitro activity than ceftolozane/tazobactam and ceftazidime/avibactam against imipenem-resistant P. aeruginosa, imipenem-resistant A. baumannii and S. maltophilia isolates.

Activity of ceftolozane-tazobactam against Escherichia coli isolates from U.S. veterans (2011) in relation to co-resistance and sequence type 131 (ST131) H30 and H30Rx status

Background

Escherichia coli sequence type 131 (ST131), with its multidrug-resistance-associated H30R1 and H30Rx clonal subsets, causes most antimicrobial-resistant E. coli infections in the U.S., especially among veterans. The activity of ceftolozane-tazobactam (C/T), a new beta-lactamase inhibitor agent, against ST131 strains, and E. coli isolates from veterans, is undefined.

Methods

We determined broth microdilution MICs for C/T and five comparators–piperacillin-tazobactam (TZP) levofloxacin (LVX), gentamicin (GEN), ceftazidime (CAZ), and meropenem (MEM)–for 595 clinical E. coli isolates, collected in 2011 from 24 Veterans Affairs Medical Centers across the U.S. Categorical resistance and MICs were compared statistically with resistance category (fluoroquinolone-susceptible, fluoroquinolone-resistant, and extended-spectrum beta-lactamase [ESBL]-producing) and with PCR-defined ST131, H30R1, and H30Rx status.

Results

Resistance prevalence was ≤ 6% for C/T (6%) and MEM (0%), vs. from 8.0% (TZP) to 59% (LVX) for the other comparators. MICs generally increased by resistance category, from fluoroquinolone-susceptible through fluoroquinolone-resistant to ESBL, and by clonal subgroup, from non-ST131-H30 through H30R1 to H30Rx. For each comparator agent except MEM, although a significantly greater fraction of resistant than susceptible isolates were C/T-resistant, only a minority of comparator-resistant isolates were C/T-resistant (i.e., 9% if LEV-resistant, 12% if GEN-resistant, 21% if CAZ-resistant, 38% if TZP-resistant).

Conclusions

C/T was broadly active against E. coli clinical isolates from veterans, notwithstanding significant variation by resistance category and ST131-H30R1/H30Rx status, outperforming all non-carbapenem comparators. C/T should prove useful as a carbapenem-sparing therapy for multidrug-resistant E. coli ST131 infections, including in veterans.