In vitro activity of ceftazidime/avibactam, cefiderocol, meropenem/vaborbactam and imipenem/relebactam against clinical strains of the Stenotrophomonas maltophilia complex

BACKGROUND

Infections caused by Stenotrophomonas maltophilia and related species are increasing worldwide. Unfortunately, treatment options are limited, whereas the antimicrobial resistance is increasing.

METHODS

We included clinical isolates identified as S. maltophilia by VITEK 2 Compact. Ceftazidime/avibactam, meropenem/vaborbactam, imipenem/relebactam, cefiderocol, quinolones, and tetracycline family members were evaluated by broth microdilution method and compared with first-line treatment drugs. Minimum inhibitory concentrations (MICs) were reported for all antibiotics. We sequenced the Whole Genome of cefiderocol resistant strains (CRSs) and annotated their genes associated with cefiderocol resistance (GACR). Presumptive phylogenetic identification employing the 16S marker was performed.

RESULTS

One hundred and one clinical strains were evaluated, sulfamethoxazole and trimethoprim, levofloxacin and minocycline showed susceptibilities of 99.01%, 95.04% and 100% respectively. Ceftazidime was the antibiotic with the highest percentage of resistance in all samples (77.22%). Five strains were resistant to cefiderocol exhibiting MIC values ≥ 2 μg/mL (4.95%). The β-lactamase inhibitors meropenem/vaborbactam and imipenem/relebactam, failed to inhibit S. maltophilia, preserving both MIC50 and MIC90 ≥64 μg/mL. Ceftazidime/avibactam restored the activity of ceftazidime decreasing the MIC range. Tigecycline had the lowest MIC range, MIC50 and MIC90. Phylogeny based on 16S rRNA allowed to identify to cefiderocol resistant strains as putative species clustered into Stenotrophomonas maltophilia complex (Smc). In these strains, we detected GARCs such as Mutiple Drug Resistance (MDR) efflux pumps, L1-type β-lactamases, iron transporters and type-1 fimbriae.

CONCLUSION

Antimicrobial resistance to first-line treatment is low. The in vitro activity of new β-lactamase inhibitors against S. maltophilia is poor, but avibactam may be a potential option. Cefiderocol could be considered as a potential new option for multidrug resistant infections. Tetracyclines had the best in vitro activity of all antibiotics evaluated.

In vitro activity of meropenem-vaborbactam plus aztreonam against metallo-β-lactamase-producing Klebsiella pneumoniae

We evaluated the in vitro activity of meropenem-vaborbactam plus aztreonam (MEV-ATM) against 140 metallo-β-lactamase (MBL)-producing Klebsiella pneumoniae isolates. Among them, 25 isolates (17.9%) displayed minimum inhibitory concentrations (MIC) ≥ 8 µg/mL, while 112 (80.0%) had MIC ≤ 2 µg/mL. Genomic analysis and subsequent gene cloning experiments revealed OmpK36 134-135GD-insertion and increased carbapenemase gene (blaNDM-1 and blaOXA-48-like) copy numbers are the main factors responsible for MEV-ATM non-susceptibility. Notably, MEV-ATM is actively against aztreonam-avibactam-resistant mutants due to CMY-16 mutations.

Effect of modification of penicillin-binding protein 3 on susceptibility to ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and cefiderocol of Escherichia coli strains producing broad-spectrum β-lactamases

The impact of penicillin-binding protein 3 (PBP3) modifications that may be identified in Escherichia coli was evaluated with respect to susceptibility to β-lactam/β-lactamase inhibitor combinations including ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and to cefiderocol. A large series of E. coli recombinant strains producing broad-spectrum β-lactamases was evaluated. While imipenem-relebactam showed a similar activity regardless of the PBP3 background, susceptibility to other molecules tested was affected at various levels. This was particularly the case for ceftazidime-avibactam, aztreonam-avibactam, and cefepime-taniborbactam.

The pharmacokinetics/pharmacodynamics of ceftazidime/avibactam for central nervous system infections caused by carbapenem-resistant Gram-negatives: a prospective study

OBJECTIVES

To describe the pharmacokinetics/pharmacodynamics (PK/PD) of ceftazidime/avibactam in critically ill patients with CNS infections.

METHODS

A prospective study of critically ill patients with CNS infections who were treated with ceftazidime/avibactam and the steady-state concentration (Css) of ceftazidime/avibactam in serum and/or CSF was conducted between August 2020 and May 2023. The relationship between PK/PD goal achievement, microbial eradication and the clinical efficacy of ceftazidime/avibactam was evaluated.

RESULTS

Seven patients were finally included. The ceftazidime/avibactam target attainment in plasma was optimal for three, quasi-optimal for one and suboptimal for three. In three patients with CSF drug concentrations measured, ceftazidime/avibactam target attainment in CSF was 100% (3/3), which was optimal. The AUCCSF/serum values were 0.59, 0.44 and 0.35 for ceftazidime and 0.57, 0.53 and 0.51 for avibactam. Of the seven patients, 100% (7/7) were treated effectively, 71.4% (5/7) achieved microbiological eradication, 85.7% (6/7) survived and 14.3% (1/7) did not survive.

CONCLUSIONS

The limited clinical data suggest that ceftazidime/avibactam is effective in the treatment of CNS infections caused by MDR Gram-negative bacilli (MDR-GNB), can achieve the ideal drug concentration of CSF, and has good blood-brain barrier penetration.

High ceftazidime-avibactam resistance among carbapenem-resistant Enterobacter species: Data from the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme, 2014-2021

OBJECTIVES

Trends in the susceptibility to ceftazidime-avibactam (CZA) and tigecycline (TGC) among Enterobacter species from different geographic areas are unknown.This study aimed to analyse the trends in CZA and TGC susceptibility changes across different continents from 2014 to 2021 utilizing Antimicrobial Testing Leadership and Surveillance (ATLAS) data.

METHODS

A total of 23 669 isolates of Enterobacter species were collected over an 8-y period.

RESULTS

The overall non-susceptibility rate of Enterobacter isolates to both CZA and TGC was 3.2%. India (16.5%), Guatemala (15.4%), and the Philippines (13.1%) exhibited the highest resistance to CZA. The increase in CZA resistance rates was particularly evident in Asia, with an increase from 4.0% to 8.3%, and in Latin America, from 1.5% to 5%. The non-susceptibility rate for TGC mildly increased in Africa/Middle East but decreased in other continents during the study period. The overall rate of carbapenem resistance increased from 2.9% in 2014-2017 to 4.3% in 2018-2021. Among carbapenem-resistant Enterobacter isolates, the CZA resistance rate was highest in Asia (87.4%), followed by Europe (69.2%) and Africa/Middle East (60.8%). Among the 380 Enterobacter isolates resistant to CZA and carbapenem, the most common genotype of carbapenemase genes was blaNDM (59.2%), followed by blaVIM (24.2%), blaOXA (4.2%), blaIMP (1.1%), and blaKPC (1.1%). The susceptibility of carbapenem-resistant Enterobacter to TGC remained high, with an overall susceptibility rate of 90%.

CONCLUSIONS

The heterogeneous distribution of CZA resistance rates among different geographical regions highlights the divergent therapeutic options for drug-resistant Enterobacter species.

Global trends in nonsusceptibility rates of Escherichia coli isolates to meropenem and ceftazidime/avibactam: Data from the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme, 2014-21

OBJECTIVE

To understand the global changes in the nonsusceptibility rates of Escherichia coli to meropenem and ceftazidime-avibactam (CZA), we conducted a study using the Antimicrobial Testing Leadership and Surveillance database.

METHODS

A total of 49 394 E. coli isolates were collected during the 8-year study period.

RESULT

The countries with the highest nonsusceptible rates for meropenem were India (16.6%), followed by Pakistan (6.7%), Ukraine (5.4%), Qatar (5.3%), and Guatemala (3.2%). For CZA, the nonsusceptible rate was highest in India (15.6%), followed by Qatar (4.0%), Guatemala (3.9%), China (2.6%), and Thailand (2.5%). During the study period, the nonsusceptible rates of meropenem and CZA in E. coli increased in Asia, Latin America, and Africa/Middle East. Isolates from the medical ICU (odds ratio [OR], 4.62) and surgical ICU (OR, 3.98) were associated with a higher risk of CZA nonsusceptible rates. Compared to intestinal specimens, respiratory and genitourinary specimens had the highest OR (2.32 and 2.17) associated with CZA resistance. Further analysis of carbapenemase distribution showed an increase in the percentage of blaNDM-positive isolates and a decrease in blaKPC-positive isolates worldwide, especially in Latin America. Additionally, we observed a gradual decline in the prevalence of blaOXA-positive E. coli without concomitant carriage of metallo-β-lactamase genes in the worldwide surveillance.

CONCLUSIONS

Further surveillance is necessary to determine whether blaNDM -positive E. coli (i.e., CZA-resistant isolates) is increasing and leading to more superbugs spreading worldwide.

Activity of aztreonam-avibactam against Enterobacterales resistant to recently approved beta-lactamase inhibitor combinations collected in Europe, Latin America, and the Asia-Pacific Region (2020-2022)

BACKGROUND

Aztreonam-avibactam is under clinical development for treatment of infections caused by carbapenem-resistant Enterobacterales (CRE), especially those resistant to recently approved β-lactamase inhibitor combinations (BLICs).

OBJECTIVES

To evaluate a large collection of CRE isolates, including those non-susceptible to ceftazidime-avibactam, meropenem-vaborbactam, and/or imipenem-relebactam.

METHODS

Overall, 24 580 Enterobacterales isolates were consecutively collected (1/patient) in 2020-2022 from 64 medical centres located in Western Europe (W-EU), Eastern Europe (E-EU), Latin America (LATAM), and the Asia-Pacific region (APAC). Of those, 1016 (4.1%) were CRE. Isolates were susceptibility tested by broth microdilution. CRE isolates were screened for carbapenemase genes by whole genome sequencing.

RESULTS

Aztreonam-avibactam inhibited 99.6% of CREs at ≤8 mg/L. Ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam were active against 64.6%, 57.4%, and 50.7% of CRE isolates, respectively; most of the non-susceptible isolates carried metallo-beta-lactamases. Aztreonam-avibactam was active against ≥98.9% of isolates non-susceptible to these BLICs. The activity of these BLICs varied by region, with highest susceptibility rates observed in W-EU (76.9% for ceftazidime-avibactam, 72.5% for meropenem-vaborbactam, 63.8% for imipenem-relebactam) and the lowest susceptibility rates identified in the APAC region (39.9% for ceftazidime-avibactam, 37.8% for meropenem-vaborbactam, and 27.5% for imipenem-relebactam). The most common carbapenemase types overall were KPC (44.6% of CREs), NDM (29.9%), and OXA-48-like (16.0%). KPC predominated in LATAM (64.1% of CREs in the region) and W-EU (61.1%). MBL occurrence was highest in APAC (59.5% of CREs in the region), followed by LATAM (34.0%), E-EU (28.9%), and W-EU (23.6%).

CONCLUSIONS

Aztreonam-avibactam demonstrated potent activity against CRE isolates resistant to ceftazidime-avibactam, meropenem-vaborbactam, and/or imipenem-relebactam independent of the carbapenemase produced.

The mechanism of ceftazidime and cefiderocol hydrolysis by D179Y variants of KPC carbapenemases is similar and involves the formation of a long-lived covalent intermediate

Klebsiella pneumoniae carbapenemase (KPC) variants have been described that confer resistance to both ceftazidime-avibactam and cefiderocol. Of these, KPC-33 and KPC-31 are D179Y-containing variants derived from KPC-2 and KPC-3, respectively. To better understand this atypical phenotype, the catalytic mechanism of ceftazidime and cefiderocol hydrolysis by KPC-33 and KPC-31 as well as the ancestral KPC-2 and KPC-3 enzymes was studied. Steady-state kinetics showed that the D179Y substitution in either KPC-2 or KPC-3 is associated with a large decrease in both kcat and KM such that kcat/KM values were largely unchanged for both ceftazidime and cefiderocol substrates. A decrease in both kcat and KM is consistent with a decreased and rate-limiting deacylation step. We explored this hypothesis by performing pre-steady-state kinetics and showed that the acylation step is rate-limiting for KPC-2 and KPC-3 for both ceftazidime and cefiderocol hydrolysis. In contrast, we observed a burst of acyl-enzyme formation followed by a slow steady-state rate for the D179Y variants of KPC-2 and KPC-3 with either ceftazidime or cefiderocol, indicating that deacylation of the covalent intermediate is the rate-limiting step for catalysis. Finally, we show that the low KM value for ceftazidime or cefiderocol hydrolysis of the D179Y variants is not an indication of tight binding affinity for the substrates but rather is a reflection of the deacylation reaction becoming rate-limiting. Thus, the hydrolysis mechanism of ceftazidime and cefiderocol by the D179Y variants is very similar and involves the formation of a long-lived covalent intermediate that is associated with resistance to the drugs.

Meropenem-ANT3310, a unique β-lactam-β-lactamase inhibitor combination with expanded antibacterial spectrum against Gram-negative pathogens including carbapenem-resistant Acinetobacter baumannii

ANT3310 is a novel broad-spectrum diazabicyclooctane serine β-lactamase inhibitor being developed in combination with meropenem (MEM) for the treatment of serious infections in hospitalized patients where carbapenem-resistant Gram-negative pathogens are expected. In this study, we evaluated the in vitro antibacterial activity of MEM in the presence of ANT3310 at 8 µg/mL against global clinical isolates that included Acinetobacter baumannii (n = 905), carbapenem-resistant Enterobacterales (CRE), carrying either oxacillinase (OXA) (n = 252) or Klebsiella pneumoniae carbapenemase (KPC) (n = 180) carbapenemases, and Pseudomonas aeruginosa (n = 502). MEM was poorly active against A. baumannii, as were MEM-vaborbactam, ceftazidime-avibactam, aztreonam-avibactam, cefepime-taniborbactam, cefepime-zidebactam, and imipenem-relebactam (MIC90 values of ≥32 µg/mL). On the other hand, MEM-ANT3310 displayed an MIC90 value of 4 µg/mL, similar to that observed with sulbactam-durlobactam, a drug developed to specifically treat A. baumannii infections. ANT3310 (8 µg/mL) additionally restored the activity of MEM against OXA- and KPC-producing CREs decreasing MEM MIC90 values from >32 µg/mL to 0.25 and 0.5 µg/mL, respectively. The combination of 8 µg/mL of both MEM and ANT3310 prevented growth of 97.5% of A. baumannii and 100% of OXA- and KPC-positive CREs, with ~90% of P. aeruginosa isolates also displaying MEM MICs ≤8 µg/mL. Furthermore, MEM-ANT3310 was efficacious in both thigh and lung murine infection models with OXA-23 A. baumannii. This study demonstrates the potent in vitro activity of the MEM-ANT3310 combination against both carbapenem-resistant A. baumannii and Enterobacterales clinical isolates, a key differentiator to other β-lactam/β-lactamase combinations.

In vitro activity of aztreonam-avibactam and comparators against Metallo-β-Lactamase-producing Enterobacterales from ATLAS Global Surveillance Program, 2016-2020

OBJECTIVES

Metallo-β-lactamase (MBL)-producing Enterobacterales are a major challenge worldwide due to limited treatment options. Aztreonam-avibactam (ATM-AVI), which is under clinical development, has shown activity against MBL-positive isolates. This study evaluated the prevalence of MBL producers and the nature of enzymes among a global collection of clinical isolates of Enterobacterales from the Antimicrobial Testing Leadership and Surveillance program (ATLAS) surveillance program (2016-2020), and the antimicrobial activity of ATM-AVI and comparators against this collection.

METHODS

Non-duplicate clinical isolates of Enterobacterales (N = 106 686) collected across 63 countries were analysed. Antimicrobial susceptibility was performed using broth microdilution. Minimum inhibitory concentrations (MICs) were interpreted using Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing breakpoints. Provisional pharmacokinetic/pharmacodynamic breakpoint of ≤8 mg/L was considered for ATM-AVI. β-lactamase genes were characterized by polymerase chain reaction and sequencing. The Cochran Armitage Trend test was used to determine significant trends in percentage of isolates over time.

RESULTS

Overall, MBL-positive isolates were 1.6% of total Enterobacterales isolates globally, with a significant increasing trend observed over time, globally and across regions (P < 0.05). New Delhi MBL (NDM) was the most common MBL (83.3%). ATM-AVI demonstrated potent activity against MBL-positive isolates (MIC ≤8 mg/L: 99.4% isolates inhibited; MIC90, 1 mg/L). Consistent activity was also noted across different regions. Potent activity was demonstrated against different NDM variants and MBL-positive isolates co-carrying other carbapenemases (98.1% and 99.7% isolates inhibited at ≤8 mg/L, respectively). About 0.6% MBL-positive isolates (10/1707) had MICs >8 mg/L for ATM-AVI.

CONCLUSION

ATM-AVI demonstrated potent activity against MBL-positive isolates, including NDM variants and MBL-positive isolates co-carrying other carbapenemases, and may represent a good option for treating infections caused by MBL-positive Enterobacterales.

Moving towards a standardized definition of antimicrobial resistance: a comparison of the antimicrobial susceptibility profile of difficult-to-treat resistance (DTR) versus multidrug-resistant (MDR) Pseudomonas aeruginosa clinical isolates (CANWARD, 2016-2021)

Pseudomonas aeruginosa clinical isolates demonstrating difficult-to-treat resistance (DTR) and multidrug-resistant (MDR) phenotypes were evaluated by broth microdilution. Susceptibility was lower for all antimicrobials versus DTR relative to MDR isolates. Ceftazidime-avibactam, ceftolozane-tazobactam, and imipenem-relebactam susceptibility was 35.9%, 64.5%, and 47.0% for DTR isolates and 60.5%, 80.6%, and 71.5% for MDR isolates.

A descriptive pharmacokinetic/pharmacodynamic analysis of ceftazidime-avibactam in a case series of critically ill patients with augmented renal clearance

To describe the pharmacokinetics/pharmacodynamics (PK/PD) of a 2 h infusion of ceftazidime-avibactam (CAZ-AVI) in critically ill patients with augmented renal clearance (ARC). A retrospective review of all critically ill patients with ARC who were treated with CAZ-AVI between August 2020 and May 2023 was conducted. Patients whose 12-h creatinine clearance prior to CAZ-AVI treatment and steady-state concentration (Css) of CAZ-AVI were both monitored were enrolled. The free fraction (fCss) of CAZ-AVI was calculated from Css. The joint PK/PD targets of CAZ-AVI were considered optimal when a Css/minimum inhibitory concentration (MIC) ratio for CAZ ≥4 (equivalent to 100% fT > 4 MIC) and a Css/CT ratio of AVI >1 (equivalent to 100% fT > CT 4.0 mg/L) were reached simultaneously, quasioptimal when only one of the two targets was reached, and suboptimal when neither target was reached. The relationship between PK/PD goal achievement, microbial eradication and the clinical efficacy of CAZ-AVI was evaluated. Four patients were included. Only one patient achieved optimal joint PK/PD targets, while the other three reached suboptimal targets. The patient with optimal PK/PD targets achieved microbiological eradication, while the other three patients did not, but all four patients achieved good clinical efficacy. Standard dosages may not enable most critically ill patients with ARC to reach the optimal joint PK/PD targets of CAZ-AVI. Optimal drug dose adjustment of CAZ-AVI in ARC patients requires dynamic drug concentration monitoring.

Emergence of cefiderocol resistance during ceftazidime/avibactam treatment caused by a large genomic deletion, including ampD and piuCD genes, in Pseudomonas aeruginosa

We report the emergence of cefiderocol resistance during the treatment of a ST312 Pseudomonas aeruginosa respiratory infection with ceftazidime/avibactam. whole genome sequencing (WGS) revealed that resistance was caused by a large genomic deletion, including PiuDC (iron transport system) and AmpD (ampC negative regulator), driven by the integration of phage DNA. Thus, our findings alert that this type of deletion could be an efficient (two mechanisms in one step) specific cefiderocol resistance mechanism that might occur nonspecifically upon treatment with β-lactams that select for AmpC overexpression.

Therapeutic drug monitoring of ceftazidime/avibactam: why one leg is not enough to run

BACKGROUND

Therapeutic drug monitoring (TDM) is becoming an increasingly recommended approach for assessing optimal pharmacokinetic/pharmacodynamic (PK/PD) target attainment of ceftazidime/avibactam. Some authors hypothesized that the PK/PD target attainment of ceftazidime/avibactam could be assessed by means of the TDM of solely ceftazidime, since avibactam concentrations might be extrapolated based on the fixed 4:1 ceftazidime-to-avibactam ratio present in the vial. The reliability of this hypothesis could be called into question if a wide interindividual variability in the ceftazidime-to-avibactam ratio would exist among patients. This study aimed to assess the distribution of the individual ceftazidime-to-avibactam ratios in relation to renal function in a cohort of adult patients who were treated with continuous infusion ceftazidime/avibactam and underwent TDM of both ceftazidime and avibactam.

METHODS

Individual ceftazidime-to-avibactam ratio was calculated at each TDM assessment. Receiving operating characteristics (ROC) curve analysis was performed for testing the potential impact of renal function on ceftazidime-to-avibactam ratio variability.

RESULTS

A total of 188 TDM assessments were collected from 107 patients. The ceftazidime-to-avibactam ratios ranged from 1.29:1 to 13.46:1. Seventy-seven out of 188 ceftazidime-to-avibactam ratios (41.0%) were >5:1, and 36 (19.1%) were >6:1. Patients without renal dysfunction had significantly higher proportions of ceftazidime-to-avibactam ratio >5:1 (59.3% versus 23.8%; P < 0.001) and >6:1 (32.1% versus 6.3%; P < 0.001) compared with those with mild-to-severe renal dysfunction.

CONCLUSIONS

The findings may strengthen the contention that for properly assessing the PK/PD target attainment of ceftazidime/avibactam, both ceftazidime and avibactam concentrations should be measured, given the unpredictability of the ceftazidime-to-avibactam ratio occurring among patients.

Reviewing novel treatment options for carbapenem-resistant Enterobacterales

INTRODUCTION

Carbapenem resistant Enterobacterales (CRE) are a major threat to global health and hospital-onset CRE infections have risen during the COVID-19 pandemic. Novel antimicrobials are now available for the treatment of CRE infections. There remains an urgent need for new antimicrobials for CRE, especially for those producing metallo-β-lactamases.

AREAS COVERED

This article discusses previously published research supporting currently available novel antimicrobials for the treatment of CRE infections. Newer compounds currently being evaluated in clinical trials are covered. A literature search was conducted in PubMed over all available dates for relevant published papers and conference abstracts with the search terms, 'CRE,' 'carbapenem-resistant Enterobacterales,' 'β-lactam-β-lactamase inhibitor,' 'KPC,' 'NDM,' 'metallo-β-lactamase,' 'ceftazidime-avibactam,' 'meropenem-vaborbactam,' 'imipenem-cilastatin-relebactam,' 'cefiderocol,' 'eravacycline,' 'plazomicin,' 'taniborbactam,' 'zidebactam,' and 'nacubactam.'

EXPERT OPINION

Novel antimicrobials for CRE infections have been developed, most notably the β-lactam-β-lactamase inhibitor combinations, though treatment options for infections with metallo-β-lactamase producing Enterobacterales remain few and have limitations. Development of antibiotics with activity against metallo-β-lactamase producing Enterobacterales is eagerly awaited, and there are promising new compounds in clinical trials. Finally, more clinical research is needed to optimize and individualize treatment approaches, which will help guide antimicrobial stewardship initiatives aimed at reducing the spread of CRE and development of further resistance.

Concomitant Resistance to Cefiderocol and Ceftazidime/Avibactam in Two Carbapenemase-Producing Klebsiella pneumoniae Isolates from Two Lung Transplant Patients

In this study, we present two cases of Klebsiella pneumoniae, one KPC-33- and one NDM-1-producing, showing resistance to cefiderocol and ceftazidime/avibactam, collected in the intensive care unit of a hospital in Northern Italy from two patients who had recently undergone lung transplantation. Whole-genome sequencing was performed to investigate the molecular features of these strains.

Functional features of KPC-109, a novel 270-loop KPC-3 mutant mediating resistance to avibactam-based β-lactamase inhibitor combinations and cefiderocol

OBJECTIVES

To investigate a ceftazidime/avibactam (CZA)-resistant Klebsiella pneumoniae (NE368), isolated from a patient exposed to CZA, expressing a novel K. pneumoniae carbapenemase (KPC)-3 variant (KPC-109).

METHODS

Antimicrobial susceptibility testing was performed by reference broth microdilution. Whole-genome sequencing (WGS) analysis of NE368 was performed combining a short- and long-reads approach (Illumina and Oxford Nanopore Technologies). Functional characterization of KPC-109 was performed to investigate the impact of KPC-109 production on the β-lactam resistance phenotype of various Escherichia coli and Klebsiella pneumoniae strains, including derivatives of K. pneumoniae with OmpK35 and OmpK36 porin alterations. Horizontal transfer of the KPC-109-encoding plasmid was investigated by conjugation and transformation experiments.

RESULTS

K. pneumoniae NE368 was isolated from a patient after repeated CZA exposure, and showed resistance to CZA, fluoroquinolones, piperacillin/tazobactam, expanded-spectrum cephalosporins, amikacin, carbapenems and cefiderocol. WGS revealed the presence of a large chimeric plasmid of original structure (pKPN-NE368), encoding a novel 270-loop mutated KPC-3 variant (KPC-109; ins_270_KYNKDD). KPC-109 production mediated resistance/decreased susceptibility to avibactam-based combinations (with ceftazidime, cefepime and aztreonam) and cefiderocol, with a trade-off on carbapenem resistance. However, in the presence of porin alterations commonly encountered in high-risk clonal lineages of K. pneumoniae, KPC-109 was also able to confer clinical-level resistance to carbapenems. Resistance of NE368 to cefiderocol was likely contributed by KPC-109 production acting in concert with a mutated EnvZ sensor kinase. The KPC-109-encoding plasmid did not appear to be conjugative.

CONCLUSIONS

These findings expand current knowledge about the diversity of emerging KPC enzyme variants with 270-loop alterations that can be encountered in the clinical setting.

Activity of novel β-lactam/β-lactamase inhibitor combinations against serine carbapenemase-producing carbapenem-resistant Pseudomonas aeruginosa

BACKGROUND

Antimicrobial resistance in Pseudomonas aeruginosa is complex and multifaceted. While the novel β-lactamase inhibitors (BLIs) avibactam, relebactam and vaborbactam inhibit serine-based β-lactamases, the comparative potency of the novel β-lactam (BL)/BLI combinations against serine carbapenemase-producing P. aeruginosa is unknown.

OBJECTIVES

To compare the in vitro activity of ceftazidime/avibactam, ceftazidime, imipenem/relebactam, imipenem, meropenem/vaborbactam and meropenem against serine β-lactamase-producing P. aeruginosa.

METHODS

Carbapenem-resistant P. aeruginosa were collated through the Enhancing Rational Antimicrobials against Carbapenem-resistant P. aeruginosa (ERACE-PA) Global Surveillance. Isolates positive for serine-based carbapenemases were assessed. MICs were determined by broth microdilution to each novel BL/BLI and BL alone.

RESULTS

GES was the most common carbapenemase identified (n = 59) followed by KPC (n = 8). Ceftazidime/avibactam had MIC50/MIC90 values of 4/8 mg/L and 91% of isolates were susceptible. Conversely, ceftazidime alone was active against only 3% of isolates. The MIC50/MIC90 of imipenem/relebactam were 16/>16 mg/L and 13% of all isolates were defined as susceptible. Of the KPC-producing isolates, 38% were susceptible to imipenem/relebactam, compared with 0% to imipenem. The meropenem/vaborbactam MIC50/MIC90 were >16/>16 mg/L, and 6% of isolates were susceptible, which was similar to meropenem alone (MIC50/90, >8/>8 mg/L; 3% susceptible) suggesting the addition of vaborbactam cannot overcome co-expressed, non-enzymatic resistance mechanisms.

CONCLUSIONS

Among the novel BL/BLIs, ceftazidime/avibactam displayed better in vitro activity and thus is a rational treatment option for serine carbapenemase-harbouring P. aeruginosa. While imipenem/relebactam displayed some activity, particularly against isolates with blaKPC, meropenem/vaborbactam exhibited poor activity, with MICs similar to meropenem alone.

Effect of achieving bone sterilisation on bone architecture and bone marrow, in an experimental rabbit model of osteomyelitis caused by carbapenemase-producing Enterobacterales

OBJECTIVES

Natural history and treatment of bone infections caused by carbapenemase-producing Enterobacterales (CPE) are poorly defined. We evaluated the effect of treatment on the progression of subacute osteomyelitis in a rabbit model.

METHODS

Two isolates were used: a KPC-producing Klebsiella pneumoniae and an Escherichia coli harbouring blaOXA-48 and blaCTX-M15 inserts, both susceptible to gentamicin, colistin, fosfomycin, and ceftazidime-avibactam. Osteomyelitis was induced in rabbits by tibial injection of 2 × 108 colony-forming units/mL. Antibiotics were started 14 d later, for 7 d, in 6 groups of 12 rabbits. Three days after treatment completion (D24), rabbits were euthanised and bones were cultured. Bone marrow and bone architecture macroscopic changes were evaluated through analysis of pictures by investigators unaware of the rabbit treatment group and microbiological outcome, using scales ranging from 0 (normal) to 3 (severe lesions) depending on modifications.

RESULTS

Bone marrow modifications induced by local infection were similar between prematurely deceased animals and non-sterilised animals (P = 0.14) but differed significantly from animals that achieved bone sterilisation after treatment (P = 0.04). Conversely, when comparing bone deformity, rabbits who died early (n = 13) had similar bone architecture as those achieving bone sterilisation (P = 0.12), as opposed to those not sterilised after treatment (P = 0.04). After a multivariate logistic regression, bone marrow scale ≤2 was associated with bone sterilisation (P < 0.001), and bone architecture scale ≤2 was associated with bone sterilisation (adjusted odds ratio = 2.7; 95% confidence interval 1.14-6.37) and KPC infection (adjusted odds ratio = 5.1; 95% confidence interval 2.17-12.13).

CONCLUSION

Effective antibacterial treatment reduces bone architecture distortion and bone marrow changes. These variables may be used as proxy for bone sterilisation.

Natural protein engineering in the Ω-loop: the role of Y221 in ceftazidime and ceftolozane resistance in Pseudomonas-derived cephalosporinase

A wide variety of clinically observed single amino acid substitutions in the Ω-loop region have been associated with increased minimum inhibitory concentrations and resistance to ceftazidime (CAZ) and ceftolozane (TOL) in Pseudomonas-derived cephalosporinase and other class C β-lactamases. Herein, we demonstrate the naturally occurring tyrosine to histidine substitution of amino acid 221 (Y221H) in Pseudomonas-derived cephalosporinase (PDC) enables CAZ and TOL hydrolysis, leading to similar kinetic profiles (k cat = 2.3 ± 0.2 µM and 2.6 ± 0.1 µM, respectively). Mass spectrometry of PDC-3 establishes the formation of stable adducts consistent with the formation of an acyl enzyme complex, while spectra of E219K (a well-characterized, CAZ- and TOL-resistant comparator) and Y221H are consistent with more rapid turnover. Thermal denaturation experiments reveal decreased stability of the variants. Importantly, PDC-3, E219K, and Y221H are all inhibited by avibactam and the boronic acid transition state inhibitors (BATSIs) LP06 and S02030 with nanomolar IC50 values and the BATSIs stabilize all three enzymes. Crystal structures of PDC-3 and Y221H as apo enzymes and complexed with LP06 and S02030 (1.35-2.10 Å resolution) demonstrate ligand-induced conformational changes, including a significant shift in the position of the sidechain of residue 221 in Y221H (as predicted by enhanced sampling well-tempered metadynamics simulations) and extensive hydrogen bonding between the enzymes and BATSIs. The shift of residue 221 leads to the expansion of the active site pocket, and molecular docking suggests substrates orientate differently and make different intermolecular interactions in the enlarged active site compared to the wild-type enzyme.

In vitro activity of imipenem/relebactam against Pseudomonas aeruginosa isolated from patients with cystic fibrosis

Pseudomonas aeruginosa is a common multidrug-resistant pathogen in patients with cystic fibrosis (CF). The in vitro activity of imipenem/relebactam and imipenem was compared with other antipseudomonal antibiotics against 105 isolates from patients with CF from three US hospitals. Imipenem/relebactam, imipenem, meropenem, ceftazidime/avibactam, and ceftolozane/tazobactam susceptibilities were 77%, 55%, 58%, 90%, and 92%, respectively. Relebactam potentiates imipenem against CF P. aeruginosa by fourfold leading imipenem/relebactam to retain susceptibility against most isolates in this cohort.

In vitro potency of xeruborbactam in combination with multiple β-lactam antibiotics in comparison with other β-lactam/β-lactamase inhibitor (BLI) combinations against carbapenem-resistant and extended-spectrum β-lactamase-producing Enterobacterales

Recently, several β-lactam (BL)/β-lactamase inhibitor (BLI) combinations have entered clinical testing or have been marketed for use, but limited direct comparative studies of their in vitro activity exist. Xeruborbactam (XER, also known as QPX7728), which is undergoing clinical development, is a cyclic boronate BLI with potent inhibitory activity against serine (serine β-lactamase) and metallo-β-lactamases (MBLs). The objectives of this study were (i) to compare the potency and spectrum of β-lactamase inhibition by various BLIs in biochemical assays using purified β-lactamases and in microbiological assays using the panel of laboratory strains expressing diverse serine and metallo-β-lactamases and (ii) to compare the in vitro potency of XER in combination with multiple β-lactam antibiotics to that of other BL/BLI combinations in head-to-head testing against recent isolates of carbapenem-resistant Enterobacterales (CRE). Minimal inhibitory concentrations (MICs) of XER combinations were tested with XER at fixed 4 or 8 µg/mL, and MIC testing was conducted in a blinded fashion using Clinical and Laboratory Standards Institute reference methods. Xeruborbactam and taniborbactam (TAN) were the only BLIs that inhibited clinically important MBLs. The spectrum of activity of xeruborbactam included several MBLs identified in Enterobacterales, e.g., and various IMP enzymes and NDM-9 that were not inhibited by taniborbactam. Xeruborbactam potency against the majority of purified β-lactamases was the highest in comparison with other BLIs. Meropenem-xeruborbactam (MEM-XER, fixed 8 µg/mL) was the most potent combination against MBL-negative CRE with MIC90 values of 0.125 µg/mL. MEM-XER and cefepime-taniborbactam (FEP-TAN) were the only BL/BLIs with activity against MBL-producing CREs; with MEM-XER (MIC90 of 1 µg/mL) being at least 16-fold more potent than FEP-TAN (MIC90 of 16 µg/mL). MEM-XER MIC values were ≤8 µg/mL for >90% of CRE, including both MBL-negative and MBL-positive isolates, with FEP-TAN MIC of >8 µg/mL. Xeruborbactam also significantly enhanced potency of other β-lactam antibiotics, including cefepime, ceftolozane, ceftriaxone, aztreonam, piperacillin, and ertapenem, against clinical isolates of Enterobacterales that carried various class A, class C, and class D extended-spectrum β-lactamases and carbapenem-resistant Enterobacterales, including metallo-β-lactamase-producing isolates. These results strongly support further clinical development of xeruborbactam combinations.

Molecular drivers of resistance to sulbactam-durlobactam in contemporary clinical isolates of Acinetobacter baumannii

Acinetobacter baumannii-calcoaceticus complex (ABC) causes severe infections that are difficult to treat due to pre-existing antibiotic resistance. Sulbactam-durlobactam (SUL-DUR) is a targeted β-lactam/β-lactamase inhibitor combination antibiotic designed to treat serious infections caused by Acinetobacter, including multidrug- and carbapenem-resistant strains. In a recent global surveillance study of 5,032 ABC clinical isolates collected from 2016 to 2021, less than 2% of ABC isolates had SUL-DUR MIC values >4 µg/mL. Molecular characterization of these isolates confirmed the primary drivers of resistance are metallo-β-lactamases or penicillin-binding protein 3 (PBP3) mutations, as previously described. In addition, this study shows that certain common PBP3 variants, such as A515V, are insufficient to confer sulbactam resistance and that the efflux of durlobactam by AdeIJK is likely to play a role in a subset of strains.

Could an optimized joint pharmacokinetic/pharmacodynamic target attainment of continuous infusion ceftazidime-avibactam be a way to avoid the need for combo therapy in the targeted treatment of deep-seated DTR Gram-negative infections?

The objective of this study was to assess the relationship between joint pharmacokinetic/pharmacodynamic (PK/PD) target attainment of continuous infusion (CI) ceftazidime-avibactam and the microbiological outcome of documented difficult-to-treat resistant (DTR) Gram-negative infections. A 2-year retrospective cohort study was performed in patients receiving CI ceftazidime-avibactam mono- or combo therapy for documented DTR Gram-negative infections and undergoing therapeutic drug monitoring of both ceftazidime and avibactam. The free fractions of steady-state concentrations (fCss) of ceftazidime and avibactam were calculated. The joint PK/PD target was considered optimal when both the fCss/MIC ratio for ceftazidime ≥4 (equivalent to 100% fT>4xMIC) and the fCss/CT ratio for avibactam >1 (equivalent to 100% fT >CT of 4.0 mg/L) were simultaneously achieved (quasi-optimal if only one of the two and suboptimal if neither of the two was achieved). Multivariate logistic regression analysis was applied for testing potential variables associated with microbiological failure. Fifty-eight patients were treated with CI ceftazidime-avibactam mono- (36) or combo therapy (22) for documented DTR Gram-negative infections [74.2% for primary or secondary bloodstream infections (BSIs)]. Combo therapy was administered more frequently to intensive care unit (ICU) patients (P = 0.023) or for pneumonia (P = 0.001) and less frequently for intra-abdominal infections and BSIs (P = 0.04). Microbiological failure occurred in five cases (8.6%, three in mono- and two in combo therapy). In the multivariate analysis, the suboptimal/quasi-optimal joint PK/PD target emerged as the only independent predictor of microbiological failure (odds ratio [OR] 11.11; 95% confidence interval [CI] 1.31-93.98; P = 0.023), whereas monotherapy was not (P = 0.99). Optimized joint PK/PD target attainment of CI ceftazidime-avibactam monotherapy could represent a way forward for allowing microbiological eradication of DTR Gram-negative infections and could render unnecessary combo therapy.

Acetylcysteine increases sensitivity of ceftazidime-avibactam-resistant enterobacterales with different enzymatic resistance to ceftazidime-avibactam in vitro and in vivo

BACKGROUND

Ceftazidime-avibactam (CZA) improves treatment outcomes for infections caused by carbapenem-resistant organisms, but has led to serious bacterial resistance. Acetylcysteine (NAC) is an approved medication that protects the respiratory tract through antioxidant and anti-inflammatory effects.

RESULTS

This study found that NAC combined with CZA effectively inhibits the growth of CZA-resistant clinical Enterobacterales strains. The CZA/NAC combination inhibits biofilm formation in vitro and decreases bacterial burden in a mouse thigh infection model. The combination is biocompatible and primarily increases cell membrane permeability to cause bacterial death.

CONCLUSIONS

These findings prove that the CZA/NAC combination has potential as a treatment for CZA-resistant Enterobacterales infections.

Hijacking a small plasmid to confer high-level resistance to aztreonam-avibactam and ceftazidime-avibactam

Acquired β-lactamase-encoding genes are typically carried by large plasmids in Gram-negative bacteria, which also commonly carry multi-copy small plasmids. This study found that mobile genetic elements carrying antimicrobial resistance genes are capable of hijacking small plasmids. This study focused on aztreonam-avibactam (ATM-AVI) as this combination can be used to effectively counter almost all β-lactamases produced by bacteria, and has been recommended against carbapenem-resistant Enterobacterales. A clinical strain (085003) of carbapenem-resistant Escherichia coli was investigated, and mutants (085003R32 and 085003R512) able to grow under 32/4 and 512/4 mg/L of ATM-AVI were obtained as representatives of low- and high-level resistance, respectively, by induction. Comparative genomics showed that 085003R32 and 085003R512 had a single nucleotide mutation of β-lactamase gene blaCMY-2, encoding a novel CMY with a Thr319Ile substitution, assigned 'CMY-2R'. Cloning and enzyme kinetics were used to verify that CMY-2R conferred ATM-AVI resistance by compromising binding of AVI and subsequent protection of ATM. Mechanisms for the discrepant resistance between 085003R32 and 085003R512 were investigated. Three tandem copies of blaCMY-2R were identified on a self-transmissible IncP1 plasmid of 085003R32 due to IS1294 misrecognizing its end terIS and rolling-circle replication. 085003R512 had only a single copy of blaCMY-2R on the IncP1 plasmid, but possessed anther blaCMY-2R on an already present 4-kb small plasmid. IS1294-mediated mobilization on to this multi-copy small plasmid increased the copy number of blaCMY-2R significantly, rendering higher resistance. This study shows that bacteria can employ multiple approaches to accommodate selection pressures imposed by exposure to varied concentrations of antimicrobial agents.

Looking for Stenotrophomonas maltophilia treatment: in vitro activity of ceftazidime/avibactam alone and in combination with aztreonam

During the Sars-Cov-2 pandemic, Stenotrophomonas maltophilia (S.maltophilia) secondary pulmonary infections have increased, especially in critically ill patients, highlighting the need for new therapeutic options. Trimethoprim-sulfamethoxazole (SXT) is the treatment of choice but the increase of resistant strains or adverse drug reactions limited its clinical use. Recently ceftazidime/avibactam (CZA) has been approved for the treatment of multi drug resistant (MDR) Gram-negative bacteria infections, including hospital acquired pneumonia. The aim of this study was to evaluate the in vitro activity of ceftazidime/avibactam (CZA) alone and in combination with aztreonam (ATM) against S. maltophilia clinical isolates by E-test method. Susceptibility of SXT and levofloxacin (LEV) was also investigated. Our results showed 22% of resistance to CZA, 2% to SXT and 26% to LEV. CZA in combination with ATM demonstrated synergistic activity against 86% of the strains, including all those resistant to CZA. The combination of CZA with ATM provides a new therapeutic option for the treatment of severe respiratory infections in critically ill patients.

In vitro activity of newer β-lactam/β-lactamase inhibitor combinations, cefiderocol, plazomicin and comparators against carbapenemase-producing Klebsiella pneumoniae isolates

Infections by carbapenem-resistant Klebsiella pneumoniae (CRKP) remain one of the greatest healthcare threats associated with significant morbidity and mortality. New antimicrobials were recently developed to address this threat. We assessed the epidemiology of carbapenemase-producing K. pneumoniae (CPKP) isolates recovered in a Greek university hospital during 2021, and their susceptibilities to old and newer antimicrobials. Minimum inhibitory concentrations (MICs) were determined by the MIC Test Strip method, except for cefiderocol (CFDC) and colistin that were evaluated by the broth microdilution method. A total of 110 CPKP strains were isolated, with KPC-producers being the most prevalent (64.6%). Among the agents tested, plazomicin (PL) displayed the highest activity against all the isolates (MIC50/MIC90, 0.5/1.5 μg/ml), followed by tigecycline (MIC50/MIC90, 1.5/4 μg/ml). All KPC-producing K. pneumoniae were susceptible to ceftazidime-avibactam (CAZ/AVI) and meropenem-vaborbactam (M/V) and 97.2% of them to imipenem-relebactam (I/R). Among the MBL-producing isolates, PL and CFDC exhibited the highest activity.

Aromatic Diboronic Acids as Effective KPC/AmpC Inhibitors

Over 30 compounds, including para-, meta-, and ortho-phenylenediboronic acids, ortho-substituted phenylboronic acids, benzenetriboronic acids, di- and triboronated thiophenes, and pyridine derivatives were investigated as potential β-lactamase inhibitors. The highest activity against KPC-type carbapenemases was found for ortho-phenylenediboronic acid 3a, which at the concentration of 8/4 mg/L reduced carbapenems' MICs up to 16/8-fold, respectively. Checkerboard assays revealed strong synergy between carbapenems and 3a with the fractional inhibitory concentrations indices of 0.1-0.32. The nitrocefin hydrolysis test and the whole cell assay with E. coli DH5α transformant carrying blaKPC-3 proved KPC enzyme being its molecular target. para-Phenylenediboronic acids efficiently potentiated carbapenems against KPC-producers and ceftazidime against AmpC-producers, whereas meta-phenylenediboronic acids enhanced only ceftazidime activity against the latter ones. Finally, the statistical analysis confirmed that ortho-phenylenediboronic acids act synergistically with carbapenems significantly stronger than other groups. Since the obtained phenylenediboronic compounds are not toxic to MRC-5 human fibroblasts at the tested concentrations, they can be considered promising scaffolds for the future development of novel KPC/AmpC inhibitors. The complexation of KPC-2 with the most representative isomeric phenylenediboronic acids 1a, 2a, and 3a was modeled by quantum mechanics/molecular mechanics calculations. Compound 3a reached the most effective configuration enabling covalent binding to the catalytic Ser70 residue.

Rapid Aztreonam/Avibactam NP test for detection of aztreonam/avibactam susceptibility/resistance in Enterobacterales

Aztreonam-avibactam (AZA), a newly developed β-lactam/β-lactamase inhibitor combination, is a treatment option for infections due to carbapenem-resistant Enterobacterales (CRE), including metallo-ß-lactamase producers, regardless of additional production of broad-spectrum serine-ß-lactamases. However, AZA-resistance has already been reported in Enterobacterales and its early detection could be a valuable tool for faster and more accurate clinical decision-making. We therefore developed a rapid culture-based test for the identification of AZA resistance among multidrug-resistant Enterobacterales. The Rapid Aztreonam/Avibactam NP test is based on resazurin reduction when bacterial growth occurs in the presence of AZA at 8/4 µg/mL (protocol 1) or 12/4 µg/mL (protocol 2). Given the absence of guidelines on AZA susceptibility testing, two tentative breakpoints were indeed used to categorize AZA-susceptible isolates: ≤4 µg/mL in protocol 1 and ≤ 8 µg/mL in protocol 2. Bacterial growth was visually detectable by a blue-to-purple or blue-to-pink color change of the medium. A total of 78 enterobacterial isolates (among which 34 AZA-resistant and 13 AZA-resistant according to protocols 1 and 2, respectively) were used to evaluate the test performance using protocol 1 or protocol 2. The sensitivity and specificity of the test were found to be 100% and 97.7%, respectively, following protocol 1 and 100% and 100%, respectively, following protocol 2, in comparison with broth microdilution. All results were obtained within 4.5 hours corresponding to a time saving of ca. 14 hours compared with currently available methods for AZA susceptibility testing. The Rapid Aztreonam/Avibactam NP test is rapid, highly sensitive, specific, easily interpretable, and easy to implement in routine.

Exploring avibactam and relebactam inhibition of Klebsiella pneumoniae carbapenemase D179N variant: role of the Ω loop-held deacylation water

Klebsiella pneumoniae carbapenemase-2 (KPC-2) presents a clinical threat as this β-lactamase confers resistance to carbapenems. Recent variants of KPC-2 in clinical isolates contribute to concerning resistance phenotypes. Klebsiella pneumoniae expressing KPC-2 D179Y acquired resistance to the ceftazidime/avibactam combination affecting both the β-lactam and the β-lactamase inhibitor yet has lowered minimum inhibitory concentrations for all other β-lactams tested. Furthermore, Klebsiella pneumoniae expressing the KPC-2 D179N variant also manifested resistance to ceftazidime/avibactam yet retained its ability to confer resistance to carbapenems although significantly reduced. This structural study focuses on the inhibition of KPC-2 D179N by avibactam and relebactam and expands our previous analysis that examined ceftazidime resistance conferred by D179N and D179Y variants. Crystal structures of KPC-2 D179N soaked with avibactam and co-crystallized with relebactam were determined. The complex with avibactam reveals avibactam making several hydrogen bonds, including with the deacylation water held in place by Ω loop. These results could explain why the KPC-2 D179Y variant, which has a disordered Ω loop, has a decreased affinity for avibactam. The relebactam KPC-2 D179N complex revealed a new orientation of the diazabicyclooctane (DBO) intermediate with the scaffold piperidine ring rotated ~150° from the standard DBO orientation. The density shows relebactam to be desulfated and present as an imine-hydrolysis intermediate not previously observed. The tetrahedral imine moiety of relebactam interacts with the deacylation water. The rotated relebactam orientation and deacylation water interaction could potentially contribute to KPC-mediated DBO fragmentation. These results elucidate important differences that could aid in the design of novel β-lactamase inhibitors.

The in vitro effect of new combinations of carbapenem-β-lactamase inhibitors for Mycobacterium abscessus

As new treatment alternatives for Mycobacterium abscessus complex (MABC) are urgently needed, we determined the minimum inhibitory concentrations (MICs) for novel carbapenem combinations, including imipenem-relebactam and tebipenem-avibactam against 98 MABC isolates by broth microdilution. The MIC50 was reduced from 16 to 8 mg/L by adding relebactam to imipenem, while the addition of avibactam to tebipenem showed a more pronounced reduction from 256 to 16 mg/L, representing a promising non-toxic, oral treatment option for further exploration.

An improved PKPD modeling approach to characterize the pharmacodynamic interaction over time between ceftazidime/avibactam and colistin from in vitro time-kill experiments against multidrug-resistant Klebsiella pneumoniae isolates

In contrast to the checkerboard method, bactericidal experiments [time-kill curves (TKCs)] allow an assessment of pharmacodynamic (PD) interactions over time. However, TKCs in combination pose interpretation problems. The objective of this study was to characterize the PD interaction over time between ceftazidime/avibactam (CZA) and colistin (CST) using TKC against four multidrug-resistant Klebsiella pneumoniae susceptible to both antibiotics and expressing a widespread carbapenemase determinant KPC-3. In vitro TKCs were performed and analyzed using pharmacokinetic/pharmacodynamic (PKPD) modeling. The general pharmacodynamic interaction model was used to characterize PD interactions between drugs. The 95% confidence intervals (95%CIs) of the expected additivity and of the observed interaction were built using parametric bootstraps and compared to evaluate the in vitro PD interaction over time. Further simulations were conducted to investigate the effect of the combination at varying concentrations typically observed in patients. Regrowth was observed in TKCs at high concentrations of drugs alone [from 4 to 32× minimum inhibitory concentrations (MIC)], while the combination systematically prevented the regrowth at concentrations close to the MIC. Significant synergy or antagonism were observed under specific conditions but overall 95%CIs overlapped widely over time indicating an additive interaction between antibiotics. Moreover, simulations of typical PK profile at standard dosages indicated that the interaction should be additive in clinical conditions. The nature of the PD interaction varied with time and concentration in TKC. Against the four K. pneumoniae isolates, the bactericidal effect of CZA + CST combination was predicted to be additive and to prevent the emergence of resistance at clinical concentrations.

Impact of acquired broad-spectrum β-lactamases on susceptibility to oral penems/carbapenems (tebipenem, sulopenem, and faropenem) alone or in combination with avibactam and taniborbactam β-lactamase inhibitors in Escherichia coli

The impact of β-lactamases on susceptibility to oral penems/carbapenems (tebipenem, sulopenem, and faropenem) and other carbapenem molecules was evaluated in Escherichia coli, alone and in combination with avibactam or taniborbactam β-lactamase inhibitors. Tebipenem and sulopenem exhibited a similar spectrum of activity compared to the intravenous carbapenems and displayed lower MIC values than ceftibuten-avibactam against E. coli producing extended-spectrum β-lactamases or AmpC enzymes. Combined with taniborbactam, tebipenem and sulopenem exhibited low MIC values against almost all tested recombinant E. coli, including metallo-β-lactamase producers.

Evaluation of in vitro pharmacodynamic drug interactions of ceftazidime/avibactam and fosfomycin in Escherichia coli

BACKGROUND

Combination therapy can increase efficacy of antibiotics and prevent emergence of resistance. Ceftazidime/avibactam and fosfomycin may be empirically combined for this purpose, but a systematic and quantitative evaluation of this combination is needed.

OBJECTIVES

In this study, a systematic analysis of the pharmacodynamic interactions of ceftazidime/avibactam and fosfomycin in clinical and isogenic Escherichia coli strains carrying genes coding for several carbapenemases or ESBLs was performed and pharmacodynamic interactions were quantified by modelling and simulations.

METHODS

Pharmacodynamic interactions were evaluated in 'dynamic' chequerboard experiments with quantification of viable bacteria in eight isogenic and six clinical E. coli strains. Additionally, supplemental time-kill experiments were performed and genomic analyses were conducted on representative fosfomycin-resistant subpopulations. Models were fitted to all data using R and NONMEM®.

RESULTS

Synergistic drug interactions were identified for 67% of the clinical and 75% of the isogenic isolates with a mean EC50 reduction of >50%. Time-kill experiments confirmed the interactions and modelling quantified EC50 reductions up to 97% in combination and synergy prevented regrowth of bacteria by enhanced killing effects. In 9 out of 12 fosfomycin-resistant mutants, genomic analyses identified previously reported mutations.

CONCLUSIONS

The broad synergistic in vitro activity of ceftazidime/avibactam and fosfomycin confirms the potential of the application of this drug combination in clinics. The substantial reduction of the EC50 in combination may allow use of lower doses or treatment of organisms with higher MIC values and encourage further research translating these findings into the clinical setting.

Mortality in KPC-producing Klebsiella pneumoniae bloodstream infections: a changing landscape

OBJECTIVES

To assess the impact of carbapenem resistance on mortality in Klebsiella pneumoniae bloodstream infection (BSI) in the era of novel β-lactam/β-lactamase inhibitor combinations.

MATERIAL AND METHODS

Retrospective study of patients with K. pneumoniae BSI between January and August 2020 in 16 centres (CARBANEW study within the MULTI-SITA project).

RESULTS

Overall, 426 patients were included: 107/426 (25%) had carbapenem-resistant K. pneumoniae (CR-Kp) BSI and 319/426 (75%) had carbapenem-susceptible K. pneumoniae (CS-Kp) BSI. Crude cumulative 30 day mortality was 33.8% and 20.7% in patients with, respectively, CR-Kp BSI and CS-Kp BSI (P = 0.027). Carbapenemase production or carbapenemase-encoding genes were detected in 84/98 tested CR-Kp isolates (85.7%), mainly KPC (78/84; 92.9%). Ceftazidime/avibactam was the most frequently used appropriate therapy for CR-Kp BSI (80/107; 74.7%). In multivariable analyses, variables showing an unfavourable association with mortality after correction for multiple testing were age-adjusted Charlson comorbidity index (HR 1.20; 95% CI 1.10-1.31, P < 0.001) and Pitt score (HR 1.33; 95% CI 1.15-1.55, P < 0.001), but not carbapenem resistance (HR 1.28, 95% CI 0.74-2.22, P = 0.410). In a propensity score-matched analysis, there was no difference in mortality between patients appropriately treated with ceftazidime/avibactam for CR-Kp BSI and patients appropriately treated with other agents (mainly meropenem monotherapy or piperacillin/tazobactam monotherapy) for CS-Kp BSI (HR 1.07; 95% CI 0.50-2.29, P = 0.866).

CONCLUSIONS

Our results suggest that the increased mortality in CR-Kp BSI compared with CS-Kp BSI is not (or no longer) dependent on the type of therapy in areas where ceftazidime/avibactam-susceptible KPC-producing isolates are the most prevalent type of CR-Kp.

High-level ceftazidime/avibactam resistance in Escherichia coli conferred by the novel plasmid-mediated β-lactamase CMY-185 variant

OBJECTIVES

To characterize a blaCMY variant associated with ceftazidime/avibactam resistance from a serially collected Escherichia coli isolate.

METHODS

A patient with an intra-abdominal infection due to recurrent E. coli was treated with ceftazidime/avibactam. On Day 48 of ceftazidime/avibactam therapy, E. coli with a ceftazidime/avibactam MIC of >256 mg/L was identified from abdominal drainage. Illumina and Oxford Nanopore Technologies WGS was performed on serial isolates to identify potential resistance mechanisms. Site-directed mutants of CMY β-lactamase were constructed to identify amino acid residues responsible for ceftazidime/avibactam resistance.

RESULTS

WGS revealed that all three isolates were E. coli ST410. The ceftazidime/avibactam-resistant strain uniquely acquired a novel CMY β-lactamase gene, herein called blaCMY-185, harboured on an IncI-γ/K1 conjugative plasmid. The CMY-185 enzyme possessed four amino acid substitutions relative to CMY-2, including A114E, Q120K, V211S and N346Y, and conferred high-level ceftazidime/avibactam resistance with an MIC of 32 mg/L. Single CMY-2 mutants did not confer reduced ceftazidime/avibactam susceptibility. However, double and triple mutants containing N346Y previously associated with ceftazidime/avibactam resistance in other AmpC enzymes, conferred ceftazidime/avibactam MICs ranging between 4 and 32 mg/L as well as reduced susceptibility to the newly developed cephalosporin, cefiderocol. Molecular modelling suggested that the N346Y substitution confers the reduction of avibactam inhibition due to steric hindrance between the side chain of Y346 and the sulphate group of avibactam.

CONCLUSIONS

We identified ceftazidime/avibactam resistance in E. coli associated with a novel CMY variant. Unlike other AmpC enzymes, CMY-185 appears to require an additional substitution on top of N346Y to confer ceftazidime/avibactam resistance.

Pharmacokinetic and Pharmacodynamic Considerations of Novel Antibiotic Agents for Pediatric Infections: A Narrative Review

Background: Currently, the escalation of microbial resistance poses a significant global challenge. Children are more susceptible to develop infections and therefore are prescribed antibiotics more frequently. The overuse and misuse of antibiotics in pediatric patients can play a considerable role in developing microbial resistance. Accordingly, many policies, including research into new antibiotic agents have been recommended to combat microbial resistance. Recent developments in novel antibiotics have shown promising results against multi-drug resistant (MDR) and extensive drug resistance (XDR) pathogens. However, as pediatric patients are typically excluded from the clinical trials of new medications, labeling and information about approved antibiotics should be improved. This study aimed to evaluate antibiotics having been introduced to the market in the last decade focusing on pediatric population. Methods: This study reviewed the published literatures on novel FDA-approved antibiotics released between 2010 and 2022. Results: Finally, seven newly approved antibiotics including ceftaroline fosamil, ceftazidime-avibactam, ceftolozane-tazobactam, ceftobiprole, imipenem-cilastatin-relebactam, meropenem-vaborbactam, and tedizolid were considered in the present review-article. All relevant data extracted from literatures, were discussed in different subtitles of "Pharmacology", "Mechanism of action", "Indication", "Dosage regimen and pharmacokinetic and pharmacodynamic properties", "Dosage adjustment in renal/liver failure", "Resistance pattern", and "Adverse drug events". Conclusion: This study reviewed available data on seven new antibiotic agents and their pharmacodynamic and pharmacokinetic properties, with a particular focus on their use in pediatric patients. The information presented in this review will be useful for healthcare professionals in selecting appropriate antibiotics for pediatric patients and for researchers in achieving the ideal therapeutic regimens.

In vitro activity of ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam alone or in combination with polymyxin B against carbapenem resistant Acinetobacter baumannii

Nosocomial infection caused by Carbapenem-Resistant Acinetobacter baumannii (CR-A. baumannii) has become a challenge in clinical practice. Acting as the last resort antibacterial agents for the treatment of CR-A. baumannii infection, polymyxins have high risk of nephrotoxicity and poor clinical efficacy. Ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam are three β-lactam/β-lactamase inhibitor combination complexes that newly approved by the Food and Drug Administration for the treatment of carbapenem-resistant Gram-negative bacterial infection. In this study, we analyzed the in vitro activity of those novel antibacterial agents alone or in combination with polymyxin B against the CR-A. baumannii obtained from a Chinese tertiary hospital. Our results suggest that those novel antibacterial agents should not be used alone for the treatment of CR-A. baumannii infection, as they cannot prevent the regrowth of bacteria at the clinical achievable blood concentration. Imipenem/relebactam and meropenem/vaborbactam should not be used as the substitutes of imipenem and meropenem for polymyxin B based combination therapy against CR-A. baumannii, since they have no edge over imipenem and meropenem on antibacterial activity when in combination with polymyxin B. Ceftazidime/avibactam may be more suitable than ceftazidime for polymyxin B based combination therapy against CR-A. baumannii, as it has a higher synergistic rate with polymyxin B, and the antibacterial activity of ceftazidime/avibactam is much higher than that of ceftazidime when tested in combination with polymyxin B. Ceftazidime/avibactam may also be the better choice than imipenem and meropenem for polymyxin B based combination therapy against CR-A. baumannii, as it has a higher synergistic rate with polymyxin B.

In vitro activity of imipenem/relebactam against non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa in the Asia-Pacific region: SMART 2017-2020

OBJECTIVES

To describe the in vitro activity of imipenem/relebactam (IMR) against non-Morganellaceae Enterobacterales (NME) and Pseudomonas aeruginosa, including piperacillin/tazobactam-nonsusceptible and meropenem-nonsusceptible isolates, infecting hospitalized patients in the Asia-Pacific region.

METHODS

From 2017 to 2020, 49 clinical laboratories in nine countries in the Asia-Pacific region participated in the SMART global surveillance program and contributed 26 783 NME and 6383 P. aeruginosa. Minimum inhibitory concentrations (MICs) were determined using CLSI broth microdilution and interpreted using CLSI M100 (2021) breakpoints. β-Lactamase genes were identified in selected isolate subsets (2017-2020) and oprD was sequenced in molecularly characterized P. aeruginosa collected in 2020.

RESULTS

Amikacin (97.9% susceptible), IMR (95.8%), meropenem (95.4%), and imipenem (92.6%) were the most active agents against NME. Among piperacillin/tazobactam-nonsusceptible NME (n=4070), 76.1% were IMR-susceptible (range by country, 97.5% [New Zealand] to 50.6% [Vietnam]); 22.4% of meropenem-nonsusceptible NME (n=1225) were IMR-susceptible (range by country, 68.8% [South Korea] to 7.6% [Thailand]). A total of 2.7% of NME carried a metallo-β-lactamase (MBL), 0.9% an OXA-48-like carbapenemase (MBL-negative), and 0.7% a KPC (MBL-negative). Amikacin (94.0% susceptible) and IMR (90.3%) were the most active agents against P. aeruginosa; 71.2% of isolates were imipenem-susceptible. Relebactam increased susceptibility to imipenem by 25.6% (from 40.5% to 66.1%) in piperacillin/tazobactam-nonsusceptible and by 44.8% (from 7.1% to 51.9%) in meropenem-nonsusceptible P. aeruginosa. Only 4.3% of P. aeruginosa were MBL-positive. A total of 70.3% (90/128) of IMR-nonsusceptible P. aeruginosa were oprD-deficient.

CONCLUSION

In 2017-2020, 96% of NME and 90% of P. aeruginosa from the Asia-Pacific region were IMR-susceptible. IMR percent susceptible rates were higher in countries with lower MBL carriage.

Multiplicity of blaKPC Genes and pKpQIL Plasmid Plasticity in the Development of Ceftazidime-Avibactam and Meropenem Coresistance in Klebsiella pneumoniae Sequence Type 307

In 2021, Klebsiella pneumoniae sequence type 307 (ST307) strains causing pulmonary and bloodstream infections identified in a hospital in Rome, Italy, reached high levels of resistance to ceftazidime-avibactam (CZA). One of these strains reached high levels of resistance to both CZA and carbapenems and carried two copies of blaKPC-3 and one copy of blaKPC-31 located on plasmid pKpQIL. The genomes and plasmids of CZA-resistant ST307 strains were analyzed to identify the molecular mechanisms leading to the evolution of resistance and compared with ST307 genomes at local and global levels. A complex pattern of multiple plasmids in rearranged configurations, coresident within the CZA-carbapenem-resistant K. pneumoniae strain, was observed. Characterization of these plasmids revealed recombination and segregation events explaining why K. pneumoniae isolates from the same patient had different antibiotic resistance profiles. This study illustrates the intense genetic plasticity occurring in ST307, one of the most worldwide-diffused K. pneumoniae high-risk clones.

Biochemical and Structural Characterization of CRH-1, a Carbapenemase from Chromobacterium haemolyticum Related to KPC β-Lactamases

KPC-2 is one of the most relevant serine-carbapenemases among the carbapenem-resistant Enterobacterales. We previously isolated from the environmental species Chromobacterium haemolyticum a class A CRH-1 β-lactamase displaying 69% amino acid sequence identity with KPC-2. The objective of this study was to analyze the kinetic behavior and crystallographic structure of this β-lactamase. Our results showed that CRH-1 can hydrolyze penicillins, cephalosporins (except ceftazidime), and carbapenems with similar efficacy compared to KPC-2. Inhibition kinetics showed that CRH-1 is not well inhibited by clavulanic acid, in contrast to efficient inhibition by avibactam (AVI). The high-resolution crystal of the apoenzyme showed that CRH-1 has a similar folding compared to other class A β-lactamases. The CRH-1/AVI complex showed that AVI adopts a chair conformation, stabilized by hydrogen bonds to Ser70, Ser237, Asn132, and Thr235. Our findings highlight the biochemical and structural similarities of CRH-1 and KPC-2 and the potential clinical impact of this carbapenemase in the event of recruitment by pathogenic bacterial species.

Ceftazidime-Decorated Gold Nanoparticles: a Promising Strategy against Clinical Ceftazidime-Avibactam-Resistant Enterobacteriaceae with Different Resistance Mechanisms

Nanoparticle-based antibiotic delivery systems are essential in combating antibiotic-resistant bacterial infections arising from acquired resistance and/or biofilm formation. Here, we report that the ceftazidime-decorated gold nanoparticles (CAZ_Au NPs) can effectively kill clinical ceftazidime-avibactam-resistant Enterobacteriaceae with various resistance mechanisms. Further study of underlying antibacterial mechanisms suggests that CAZ_Au NPs can damage the bacterial cell membrane and increase the level of intracellular reactive oxygen species. Moreover, CAZ_Au NPs show great potential in inhibiting biofilm formation and eradicating mature biofilms via crystal violet and scanning electron microscope assays. In addition, CAZ_Au NPs demonstrate excellent performance in improving the survival rate in the mouse model of abdominal infection. In addition, CAZ_Au NPs show no significant toxicity at bactericidal concentrations in the cell viability assay. Thus, this strategy provides a simple way to drastically improve the potency of ceftazidime as an antibiotic and its use in further biomedical applications.

Impact of Acquired Broad Spectrum β-Lactamases on Susceptibility to Novel Combinations Made of β-Lactams (Aztreonam, Cefepime, Meropenem, and Imipenem) and Novel β-Lactamase Inhibitors in Escherichia coli and Pseudomonas aeruginosa

The impact of broad-spectrum β-lactamases on the susceptibility to novel β-lactamase/β-lactamase inhibitor combinations was evaluated both in Pseudomonas aeruginosa and Escherichia coli using isogenic backgrounds. Cefepime-zidebactam displayed low MICs, mainly due to the significant intrinsic antibacterial activity of zidebactam. Cefepime-taniborbactam showed excellent activity against recombinant E. coli strains, including metallo-β-lactamase producers, whereas aztreonam-avibactam remained the best therapeutic option against class B β-lactamase-producing P. aeruginosa.

Impact of Minor Carbapenemases on Susceptibility to Novel β-Lactam/β-Lactamase Inhibitor Combinations and Cefiderocol in Enterobacterales

The in vitro activity of imipenem-relebactam, meropenem-vaborbactam, ceftazidime-avibactam, and cefiderocol was evaluated against both clinical and isogenic enterobacterial isolates producing carbapenemases of the SME, NmcA, FRI, and IMI types. Ceftazidime-avibactam and meropenem-vaborbactam showed the highest activity against all tested isolates; imipenem-relebactam showed only moderate activity. All isolates remained susceptible to cefiderocol. Furthermore, avibactam and vaborbactam have greater inhibitory activity than relebactam against the tested carbapenemases. Overall, ceftazidime-avibactam, meropenem-vaborbactam, and cefiderocol were the most effective therapeutic options for treating infections caused by the tested minor carbapenemase producers.