Activities of NXL104 combinations with ceftazidime and aztreonam against carbapenemase-Producing Enterobacteriaceae

Past, present, and future perspectives on aztreonam and avibactam

INTRODUCTION

Aztreonam is a monobactam antibiotic approved in 1986 to treat infections caused by aerobic Gram-negative bacteria, but, together with cephalosporins, lost clinical utility due to the emergence of extended-spectrum β-lactamases (ESBLs) and novel (serine) carbapenemases. Avibactam was the first in a novel non-β-lactam β-lactamase inhibitor class to effectively inhibit these enzymes. It has been approved in combination with ceftazidime to treat Gram-negative infections caused by bacteria that produce AmpC, ESBLs and serine carbapenemases, and with aztreonam to treat patients infected with metallo-β-lactamase-producing enteric bacteria. Combinations of avibactam with ceftazidime and/or aztreonam have been used successfully to treat enteric pathogens producing multiple classes of β-lactamases.

AREAS COVERED

Development of aztreonam, avibactam, and avibactam combinations are placed into a historical perspective, based on both preclinical and clinical data. A search of MEDLINE (Ovid) was used to identify relevant literature.

EXPERT OPINION

Avibactam combined with ceftazidime and aztreonam in either dual or triple combinations provides the opportunity to treat previously untreatable Gram-negative infections that produce multiple β-lactamases. Aztreonam combinations should be particularly attractive, due to stability to metallo-β-lactamase hydrolysis and its safety advantage in treating penicillin-allergic patients. Other inhibitor combinations in development may challenge these combinations.

Impact of the inoculum size on the in vivo activity of the aztreonam-avibactam combination in a murine model of peritonitis due to Escherichia coli expressing CTX-M-15 and NDM-1

The combination of aztreonam (ATM) and avibactam (AVI) is an attractive option to treat infections caused by extended spectrum β-lactamase plus NDM-1-producing Enterobacteriaceae. Since ATM activity was shown to be severely impacted by an increase in the inoculum size in vitro, we wondered whether ATM-AVI activity could be impaired in high-inoculum infections. We analyzed the impact of the inoculum size on ATM-AVI activity in vitro and in a murine model of peritonitis due to susceptible Escherichia coli CFT073-pTOPO and its isogenic derivatives producing NDM-1 (E. coli CFT073-NDM1) and CTX-M-15 plus NDM-1 (E. coli CFT073-CTXM15-NDM1). The impact of the inoculum size on bacterial morphology was studied by microscopic examination. In vitro, at standard (105) inoculum, E. coli CFT073-CTXM15-NDM1 was resistant to ATM but susceptible to the ATM-AVI combination. At high (107) inoculum, MICs of ATM alone and of the ATM-AVI combination reached >512 and 64 mg/L, respectively, against all tested strains. ATM led to bacterial filamentation when active against the bacteria, i.e., in monotherapy or in combination with AVI against susceptible E. coli CFT073-pTOPO and only in combination with AVI against E. coli CFT073-CTXM15-NDM1. In vivo, increase in the inoculum led to a drastic decrease in the activity of ATM alone against E. coli CFT073-pTOPO and ATM-AVI against E. coli CFT073-CTXM15-NDM1. Our results suggest a high in vivo impact of the inoculum increase on the activity of ATM alone against ATM-susceptible E. coli and of ATM-AVI against CTX-M-15 plus NDM-1 producing E. coli. Clinicians must be aware of the risk of failures when using ATM-AVI in high-inoculum infections.

Novel plasmid-mediated CMY variant (CMY-192) conferring ceftazidime-avibactam resistance in multidrug-resistant Escherichia coli

The rapid rise of multidrug resistance (MDR) among Gram-negative bacteria has accelerated the development of novel therapies. Ceftazidime-avibactam (CZA) is a novel β-lactam/β-lactamase inhibitor recently approved for the treatment of limited infectious diseases. Here, we describe a novel CMY variant, CMY-192, that confers high-level resistance to CZA. This gene was detected in a clinical MDR Escherichia coli strain (Ec73552) isolated from an outpatient with a community-acquired urinary tract infection who had not received prior CZA treatment. Ec73552 was typed as O101:H9-ST10, a high-risk clone associated with human and animal diseases. Ec73552 was able to colonize the bladder in a mouse model, suggesting that this strain was uropathogenic. CMY-192 shared the highest amino acid identity (98.95%) with CMY-172 and conferred at least a 32-fold increase in CZA MIC (from ≤0.125/4 to 8/4 mg/L) when cloned into a CZA-susceptible E. coli DH5α strain. Knockout of CMY-192 in Ec73552 resulted in a 256-fold reduction in CZA MIC (from 64/4 to 0.25/4 mg/L). CMY-192 was encoded on an IncB/O/K/Z-type plasmid (pCMY192). Conjugation assays confirmed that pCMY192 was self-transmissible, resulting in a 256-fold increase in the CZA MIC of the recipient. Notably, pCMY192 cured in Ec73552 did not confer a growth advantage, while the conjugant exhibited reduced biomass and growth rate, indicating that fitness costs imposed by pCMY192 may have been compensated in Ec73552. Our findings highlight the importance of continuous monitoring of CZA susceptibility to prevent the spread of resistance in clinical settings.

Ceftazidime with avibactam for treating severe aerobic Gram-negative bacterial infections: technology evaluation to inform a novel subscription-style payment model

Background

To limit the use of antimicrobials without disincentivising the development of novel antimicrobials, there is interest in establishing innovative models that fund antimicrobials based on an evaluation of their value as opposed to the volumes used. The aim of this project was to evaluate the population-level health benefit of ceftazidime-avibactam in the NHS in England, for the treatment of severe aerobic Gram-negative bacterial infections when used within its licensed indications. The results were used to inform National Institute for Health and Care Excellence guidance in support of commercial discussions regarding contract value between the manufacturer and NHS England.

Methods

The health benefit of ceftazidime-avibactam was first derived for a series of high-value clinical scenarios. These represented uses that were expected to have a significant impact on patients' mortality risks and health-related quality of life. Patient-level costs and health-related quality of life of ceftazidime-avibactam under various usage scenarios compared with alternative management strategies in the high-value clinical scenarios were quantified using decision modelling. Results were reported as incremental net health effects expressed in quality-adjusted life-years, which were scaled to 20-year population in quality-adjusted life-years using infection number forecasts based on data from Public Health England. The outcomes estimated for the high-value clinical scenarios were extrapolated to other expected uses for ceftazidime-avibactam.

Results

The clinical effectiveness of ceftazidime-avibactam relative to its comparators was estimated by synthesising evidence on susceptibility of the pathogens of interest to the antimicrobials in a network meta-analysis. In the base case, ceftazidime-avibactam was associated with a statistically significantly higher susceptibility relative to colistin (odds ratio 7.24, 95% credible interval 2.58 to 20.94). The remainder of the treatments were associated with lower susceptibility than colistin (odds ratio < 1). The results were sensitive to the definition of resistance and the studies included in the analysis. In the base case, patient-level benefit of ceftazidime-avibactam was between 0.08 and 0.16 quality-adjusted life-years, depending on the site of infection and the usage scenario. There was a high degree of uncertainty surrounding the benefits of ceftazidime-avibactam across all subgroups, and the results were sensitive to assumptions in the meta-analysis used to estimate susceptibility. There was substantial uncertainty in the number of infections that are suitable for treatment with ceftazidime-avibactam, so population-level results are presented for a range of scenarios for the current infection numbers, the expected increases in infections over time, and rates of emergence of resistance. The population-level benefit varied substantially across the scenarios, from 531 to 2342 quality-adjusted life-years over 20 years.

Conclusion

This work has provided quantitative estimates of the value of ceftazidime-avibactam within its areas of expected usage within the NHS.

Limitations

Given existing evidence, the estimates of the value of ceftazidime-avibactam are highly uncertain.

Future work

Future evaluations of antimicrobials would benefit from improvements to NHS data linkages, research to support appropriate synthesis of susceptibility studies, and application of routine data and decision modelling to assess enablement value.

Study registration

No registration of this study was undertaken.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Policy Research Programme (NIHR award ref: NIHR135592), conducted through the Policy Research Unit in Economic Methods of Evaluation in Health and Social Care Interventions, PR-PRU-1217-20401, and is published in full in Health Technology Assessment; Vol. 28, No. 73. See the NIHR Funding and Awards website for further award information.

Evolving resistance landscape in gram-negative pathogens: An update on β-lactam and β-lactam-inhibitor treatment combinations for carbapenem-resistant organisms

Antibiotic resistance has become a global threat as it is continuously growing due to the evolution of β-lactamases diminishing the activity of classic β-lactam (BL) antibiotics. Recent antibiotic discovery and development efforts have led to the availability of β-lactamase inhibitors (BLIs) with activity against extended-spectrum β-lactamases as well as Klebsiella pneumoniae carbapenemase (KPC)-producing carbapenem-resistant organisms (CRO). Nevertheless, there is still a lack of drugs that target metallo-β-lactamases (MBL), which hydrolyze carbapenems efficiently, and oxacillinases (OXA) often present in carbapenem-resistant Acinetobacter baumannii. This review aims to provide a snapshot of microbiology, pharmacology, and clinical data for currently available BL/BLI treatment options as well as agents in late stage development for CRO harboring various β-lactamases including MBL and OXA-enzymes.

Gas Chromatography-Ion Mobility Spectrometry Reveals Acetoin as a Biomarker for Carbapenemase-Producing Klebsiella pneumoniae

BACKGROUND This study aimed to detect the volatile organic compound (VOC), 3-hydroxy-2-butanone (acetoin) using gas chromatography-ion mobility spectrometry (GC-IMS) in antimicrobial-resistant Klebsiella pneumoniae (K. pneumoniae) carbapenemase (KPC)-producing bacteria. MATERIAL AND METHODS Using stromal fluid of blood culture bottles (BacT/ALERT® SA) as the medium, 3-hydroxy-2-butanone (acetoin) released by K. pneumoniae during growth was detected using GC-IMS. The impact of imipenem (IPM) and carbapenemase inhibitors [avibactam sodium or pyridine-2,6-dicarboxylic acid (DPA)] on the emission of 3-hydroxy-2-butanone (acetoin) from various carbapenemase-producing K. pneumoniae was further investigated. Subsequently, VOCal software was used to generate a pseudo-3D plot of 3-hydroxy-2-butanone (acetoin), and the relative peak volumes were exported for data analysis. Standard strains served as references, and the findings were validated with clinical isolates. RESULTS The pattern of temporal changes in the 3-hydroxy-2-butanone (acetoin) release from K. pneumoniae in the absence of IPM was consistent with the growth curve. After the IPM addition, carbapenemase-positive strains released significantly higher contents of 3-hydroxy-2-butanone (acetoin) than carbapenemase-negative strains at the late exponential growth phase (T2). Notably, adding avibactam sodium significantly decreased the 3-hydroxy-2-butanone (acetoin) content released from the class A carbapenemase-producing strains as compared to the absence of the carbapenemase inhibitor. Conversely, adding DPA significantly decreased the 3-hydroxy-2-butanone (acetoin) content released from the class B carbapenemase-producing strains (both standard and clinical strains, all P<0.05). CONCLUSIONS This study demonstrated the potential of 3-hydroxy-2-butanone (acetoin) as a VOC biomarker for detecting carbapenemase-producing K. pneumoniae, as revealed by GC-IMS analysis.

The Triple Combination of Meropenem, Avibactam, and a Metallo-β-Lactamase Inhibitor Optimizes Antibacterial Coverage Against Different β-Lactamase Producers

This work explores the potential of a triple combination of meropenem (MEM), a novel metallo-β-lactamase (MBL) inhibitor (indole-2-carboxylate 58 (InC58)), and a serine-β-lactamase (SBL) inhibitor (avibactam (AVI)) for broad-spectrum activity against carbapenemase-producing bacteria. A diverse panel comprising MBL- and SBL-producing strains was used for susceptibility testing of the triple combination using the agar dilution method. The frequency of resistance (FoR) to MEM combined with InC58 was investigated. Mutants were sequenced and tested for cross resistance, fitness, and the stability of the resistance phenotype. Compared with the double combinations of MEM plus an SBL or MBL inhibitor, the triple combination extended the spectrum of activity to most of the isolates bearing SBLs (oxacillinase-48 (OXA-48) and Klebsiella pneumoniae carbapenemase-2 (KPC-2)) and MBLs (New Delhi metallo-β-lactamases (NDMs)), although it was not effective against Verona integron-encoded metallo-β-lactamase (VIM)-carrying Pseudomonas aeruginosa (P. aeruginosa) and OXA-23-carrying Acinetobacter baumannii (A. baumannii). The FoR to MEM plus InC58 ranged from 2.22 × 10-7 to 1.13 × 10-6. The resistance correlated with mutations to ompC and comR, affecting porin C and copper permeability, respectively. The mutants manifested a fitness cost, a decreased level of resistance during passage without antibiotic pressure, and cross resistance to another carbapenem (imipenem) and a β-lactamase inhibitor (taniborbactam). In conclusion, compared with the dual combinations, the triple combination of MEM with InC58 and AVI showed a much wider spectrum of activity against different carbapenemase-producing bacteria, revealing a new strategy to combat β-lactamase-mediated antimicrobial resistance.

Dose selection for aztreonam-avibactam, including adjustments for renal impairment, for Phase IIa and Phase III evaluation

PURPOSE

A series of iterative population pharmacokinetic (PK) modeling and probability of target attainment (PTA) analyses based on emerging data supported dose selection for aztreonam-avibactam, an investigational combination antibiotic for serious Gram-negative bacterial infections.

METHODS

Two iterations of PK models built from avibactam data in infected patients and aztreonam data in healthy subjects with "patient-like" assumptions were used in joint PTA analyses (primary target: aztreonam 60% fT > 8 mg/L, avibactam 50% fT > 2.5 mg/L) exploring patient variability, infusion durations, and adjustments for moderate (estimated creatinine clearance [CrCL] > 30 to ≤ 50 mL/min) and severe renal impairment (> 15 to ≤ 30 mL/min). Achievement of > 90% joint PTA and the impact of differential renal clearance were considerations in dose selection.

RESULTS

Iteration 1 simulations for Phase I/IIa dose selection/modification demonstrated that 3-h and continuous infusions provide comparable PTA; avibactam dose drives joint PTA within clinically relevant exposure targets; and loading doses support more rapid joint target attainment. An aztreonam/avibactam 500/137 mg 30-min loading dose and 1500/410 mg 3-h maintenance infusions q6h were selected for further evaluation. Iteration 2 simulations using expanded PK models supported an alteration to the regimen (500/167 mg loading; 1500/500 mg q6h maintenance 3-h infusions for CrCL > 50 mL/min) and selection of doses for renal impairment for Phase IIa/III clinical studies.

CONCLUSION

A loading dose plus 3-h maintenance infusions of aztreonam-avibactam in a 3:1 fixed ratio q6h optimizes joint PTA. These analyses supported dose selection for the aztreonam-avibactam Phase III clinical program.

CLINICAL TRIAL REGISTRATION

NCT01689207; NCT02655419; NCT03329092; NCT03580044.

Role of β-Lactamase Inhibitors as Potentiators in Antimicrobial Chemotherapy Targeting Gram-Negative Bacteria

Since the discovery of penicillin, β-lactam antibiotics have commonly been used to treat bacterial infections. Unfortunately, at the same time, pathogens can develop resistance to β-lactam antibiotics such as penicillins, cephalosporins, monobactams, and carbapenems by producing β-lactamases. Therefore, a combination of β-lactam antibiotics with β-lactamase inhibitors has been a promising approach to controlling β-lactam-resistant bacteria. The discovery of novel β-lactamase inhibitors (BLIs) is essential for effectively treating antibiotic-resistant bacterial infections. Therefore, this review discusses the development of innovative inhibitors meant to enhance the activity of β-lactam antibiotics. Specifically, this review describes the classification and characteristics of different classes of β-lactamases and the synergistic mechanisms of β-lactams and BLIs. In addition, we introduce potential sources of compounds for use as novel BLIs. This provides insights into overcoming current challenges in β-lactamase-producing bacteria and designing effective treatment options in combination with BLIs.

Tackling the outer membrane: facilitating compound entry into Gram-negative bacterial pathogens

Emerging resistance to all available antibiotics highlights the need to develop new antibiotics with novel mechanisms of action. Most of the currently used antibiotics target Gram-positive bacteria while Gram-negative bacteria easily bypass the action of most drug molecules because of their unique outer membrane. This additional layer acts as a potent barrier restricting the entry of compounds into the cell. In this scenario, several approaches have been elucidated to increase the accumulation of compounds into Gram-negative bacteria. This review includes a brief description of the physicochemical properties that can aid compounds to enter and accumulate in Gram-negative bacteria and covers different strategies to target or bypass the outer membrane-mediated barrier in Gram-negative bacterial pathogens.

Development of a whole-cell biosensor for β-lactamase inhibitor discovery

The production of β-lactamases by bacterial pathogens endangers antimicrobial therapy, and new inhibitors for β-lactamases are urgently needed. We report the development of a luminescent-based biosensor that quantifies β-lactamase inhibition in a cellular context, based on the activation of transcriptional factor AmpR following the exposure of bacterial cells to β-lactams. This rapid method can account for factors like membrane permeability and can be employed to identify new β-lactamase inhibitors.

Inhibition of β-lactamase function by de novo designed peptide

Antimicrobial resistance is a great public health concern that is now described as a "silent pandemic". The global burden of antimicrobial resistance requires new antibacterial treatments, especially for the most challenging multidrug-resistant bacteria. There are various mechanisms by which bacteria develop antimicrobial resistance including expression of β-lactamase enzymes, overexpression of efflux pumps, reduced cell permeability through downregulation of porins required for β-lactam entry, or modifications in penicillin-binding proteins. Inactivation of the β-lactam antibiotics by β-lactamase enzymes is the most common mechanism of bacterial resistance to these agents. Although several effective small-molecule inhibitors of β-lactamases such as clavulanic acid and avibactam are clinically available, they act only on selected class A, C, and some class D enzymes. Currently, none of the clinically approved inhibitors can effectively inhibit Class B metallo-β-lactamases. Additionally, there is increased resistance to these inhibitors reported in several bacteria. The objective of this study is to use the Resonant Recognition Model (RRM), as a novel strategy to inhibit/modulate specific antimicrobial resistance targets. The RRM is a bio-physical approach that analyzes the distribution of energies of free electrons and posits that there is a significant correlation between the spectra of this energy distribution and related protein biological activity. In this study, we have used the RRM concept to evaluate the structure-function properties of a group of 22 β-lactamase proteins and designed 30-mer peptides with the desired RRM spectral periodicities (frequencies) to function as β-lactamase inhibitors. In contrast to the controls, our results indicate 100% inhibition of the class A β-lactamases from Escherichia coli and Enterobacter cloacae. Taken together, the RRM model can likely be utilized as a promising approach to design β-lactamase inhibitors for any specific class. This may open a new direction to combat antimicrobial resistance.

Comparative efficacy and safety of non-polymyxin antibiotics against nosocomial pneumonia, complicated intra-abdominal infection, or complicated urinary tract infection: A network meta-analysis of randomised clinical trials

OBJECTIVES

The increasing epidemic of infections caused by drug-resistant Gram-negative bacteria has led to the development of several antibiotic therapies. Owing to the scarcity of head-to-head comparisons of current and emerging antibiotics, the present network meta-analysis aimed to compare the efficacy and safety of antibiotics in patients with nosocomial pneumonia, complicated intra-abdominal infection, or complicated urinary tract infection.

METHODS

Two independent researchers systematically searched databases up to August 2022 and included 26 randomised controlled trials that fulfilled the inclusion criteria. The protocol was registered in the Prospective Register of Systematic Reviews, PROSPERO (CRD42021237798). The frequentist random effects model (R version 3.5.1, netmeta package) was utilized. The DerSimonian-Laird random effects model was used to estimate heterogeneity. The calculated P-score was applied to rank the interventions. Additionally, inconsistencies, publication bias, and subgroup effects were assessed in the present study to avoid bias.

RESULTS

There was no significant difference among included antibiotics in terms of clinical response and mortality, probably because most antibiotic trials were designed to be non-inferior. In terms of P-score ranking, carbapenems may be the recommended choice considering both adverse events and clinical responses. On the other hand, for carbapenem-sparing options, ceftolozane-tazobactam was the preferred antibiotic for nosocomial pneumonia; eravacycline, for complicated intra-abdominal infection; and cefiderocol, for complicated urinary tract infection.

CONCLUSION

Carbapenems may be preferable options in terms of safety and efficacy for the treatment of Gram-negative bacterial complicated infections. However, to preserve the effectiveness of carbapenems, it is important to consider carbapenem-sparing regimens.

Resistance to aztreonam-avibactam due to a mutation of SHV-12 in Enterobacter

Aztreonam-avibactam is an important option against Enterobacterales producing metallo-β-lactamases (MBLs). We obtained an aztreonam-avibactam-resistant mutant of an MBL-producing Enterobacter mori strain by induced mutagenesis. Genome sequencing revealed an Arg244Gly (Ambler position) substitution of SHV-12 β-lactamase in the mutant. Cloning and susceptibility testing verified that the SHV-12 Arg244Gly substitution led to significantly reduced susceptibility to aztreonam-avibactam (MIC, from 0.5/4 to 4/4 mg/L) but with the loss of resistance to cephalosporins as tradeoff. Arg244 of SHV involves in the binding of avibactam by forming an arginine-mediated salt bridge and is a critical residue to interact with β-lactams. Molecular modeling analysis demonstrated that the Arg244Gly substitution hindered the binding of avibactam to SHV with higher binding energy (from - 5.24 to -4.32 kcal/mol) and elevated inhibition constant Ki (from 143.96 to 677.37 µM) to indicate lower affinity. This substitution, however, resulted in loss of resistance to cephalosporins as tradeoff by impairing substrate binding. This represents a new aztreonam-avibactam resistance mechanism.

Prevalence and clonal diversity of carbapenem-resistant Klebsiella pneumoniae causing neonatal infections: A systematic review of 128 articles across 30 countries

BACKGROUND

Klebsiella pneumoniae is the most common pathogen causing neonatal infections, leading to high mortality worldwide. Along with increasing antimicrobial use in neonates, carbapenem-resistant K. pneumoniae (CRKP) has emerged as a severe challenge for infection control and treatment. However, no comprehensive systematic review is available to describe the global epidemiology of neonatal CRKP infections. We therefore performed a systematic review of available data worldwide and combined a genome-based analysis to address the prevalence, clonal diversity, and carbapenem resistance genes of CRKP causing neonatal infections.

METHODS AND FINDINGS

We performed a systematic review of studies reporting population-based neonatal infections caused by CRKP in combination with a genome-based analysis of all publicly available CRKP genomes with neonatal origins. We searched multiple databases (PubMed, Web of Science, Embase, Ovid MEDLINE, Cochrane, bioRxiv, and medRxiv) to identify studies that have reported data of neonatal CRKP infections up to June 30, 2022. We included studies addressing the prevalence of CRKP infections and colonization in neonates but excluded studies lacking the numbers of neonates, the geographical location, or independent data on Klebsiella or CRKP isolates. We used narrative synthesis for pooling data with JMP statistical software. We identified 8,558 articles and excluding those that did not meet inclusion criteria. We included 128 studies, none of which were preprints, comprising 127,583 neonates in 30 countries including 21 low- and middle-income countries (LMICs) for analysis. We found that bloodstream infection is the most common infection type in reported data. We estimated that the pooled global prevalence of CRKP infections in hospitalized neonates was 0.3% (95% confidence interval [CI], 0.2% to 0.3%). Based on 21 studies reporting patient outcomes, we found that the pooled mortality of neonatal CRKP infections was 22.9% (95% CI, 13.0% to 32.9%). A total of 535 neonatal CRKP genomes were identified from GenBank including Sequence Read Archive, of which 204 were not linked to any publications. We incorporated the 204 genomes with a literature review for understanding the species distribution, clonal diversity, and carbapenemase types. We identified 146 sequence types (STs) for neonatal CRKP strains and found that ST17, ST11, and ST15 were the 3 most common lineages. In particular, ST17 CRKP has been seen in neonates in 8 countries across 4 continents. The vast majority (75.3%) of the 1,592 neonatal CRKP strains available for analyzing carbapenemase have genes encoding metallo-β-lactamases and NDM (New Delhi metallo-β-lactamase) appeared to be the most common carbapenemase (64.3%). The main limitation of this study is the absence or scarcity of data from North America, South America, and Oceania.

CONCLUSIONS

CRKP contributes to a considerable number of neonatal infections and leads to significant neonatal mortality. Neonatal CRKP strains are highly diverse, while ST17 is globally prevalent and merits early detection for treatment and prevention. The dominance of blaNDM carbapenemase genes imposes challenges on therapeutic options in neonates and supports the continued inhibitor-related drug discovery.

The Clash of the Titans: COVID-19, Carbapenem-Resistant Enterobacterales, and First mcr-1-Mediated Colistin Resistance in Humans in Romania

(1) Background: Antibiotic resistance and coronavirus disease-19 (COVID-19) represent a dual challenge in daily clinical practice, inducing a high burden on public health systems. Hence, we aimed to dynamically evaluate the impact of COVID-19 on patients with carbapenem-resistant Enterobacterales (CRE) urinary tract infections (UTIs), as well as the antibiotic resistance trends after the onset of the pandemic. (2) Methods: We conducted a prospective study including patients with CRE UTIs who were enrolled both pre- and during the pandemic from 2019 to 2022. We further performed a standardized and comparative clinical, paraclinical, and microbiological assessment between patients with and without COVID-19. (3) Results: A total of 87 patients with CRE UTIs were included in this study (46 pre-pandemic and 41 during the pandemic, of which 21 had associated Severe Acute Respiratory Syndrome Coronavirus-2 infection). Klebsiella pneumoniae was the main etiological agent of the UTIs, with the majority of strains (82.7%) being carbapenemase producers (mainly OXA-48 producers), while five of the 34 colistin-resistant isolates were harboring the mobile colistin resistance-1 (mcr-1) gene. COVID-19 patients presented a significantly worse outcome with higher rates of intensive care unit (ICU) admissions (66.7% for COVID patients vs. 18.2% for non-COVID patients, p < 0.001), while the fatality rates were also considerably higher among patients with concomitant viral infection (33.3% vs. 12.1%, p < 0.001). Besides COVID-19, additional risk factors associated with increased mortality were urinary catheterization, sepsis with K. pneumoniae, impaired liver and kidney function, and an inappropriate initial empiric antibiotic therapy. (4) Conclusions: COVID-19 showed a pronounced negative impact on patients with CRE UTIs, with significantly longer hospitalizations and higher ICU admissions and mortality rates.

In Vitro Activity of Imipenem-Relebactam, Meropenem-Vaborbactam, Ceftazidime-Avibactam and Comparators on Carbapenem-Resistant Non-Carbapenemase-Producing Enterobacterales

Background: Avibactam, relebactam and vaborbactam are β-lactamase inhibitors that proved their efficiency against KPC-producing Enterobacterales. Regarding their inhibitor activity towards Ambler’s class A extended spectrum β-lactamases (ESBL) and Ambler’s class C cephalosporinase (AmpC), they should be active on most of the carbapenem-resistant non-carbapenemase-producing Enterobacterales (CR non-CPE). Objectives: Determine the in vitro activity of ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam and comparators against CR non-CPE. Methods: MICs to ceftazidime/avibactam, imipenem/relebactam, meropenem/vaborbactam, but also temocillin, ceftolozane/tazobactam, ertapenem, colistin, eravacycline and tigecycline were determined by broth microdilution (ThermoFisher) on a collection of 284 CR non-CPE (inhibition zone diameter < 22 mm to meropenem). Whole genome sequencing was performed on 90 isolates to assess the genetic diversity as well as resistome. Results: According to EUCAST breakpoints, susceptibility rates of ceftazidime, imipenem, meropenem and ertapenem used at standard dose were 0.7%, 45.1%, 14.8% and 2.5%, respectively. Increased exposure of ceftazidime, imipenem and meropenem led to reach 3.5%, 68.3% and 67.7% susceptibility, respectively. Using the EUCAST clinical breakpoints, susceptibility rates of ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam were 88.4%, 81.0% and 80.6%, respectively. Susceptibility rates of temocillin, ceftolozane/tazobactam, tigecycline, eravacycline, and colistin were 0%, 4.6%, 27.8%, 54.9% and 90.1%. MICs distributions with and without the presence of the inhibitor demonstrated a better ability of avibactam and relebactam compared to vaborbactam to restore susceptibility to the associated β-lactam. Conclusions: This study demonstrated the in vitro efficacy of ceftazidime/avibactam, imipenem/relebactam and to a lesser extent meropenem/vaborbactam against CR non-CPE. Moreover, to test all β-lactams/β-lactamases inhibitors combinations without a priori for CRE, non-CPE is crucial since resistance to one of the β-lactam/β-lactamase inhibitor combinations does not predict resistance to another molecule, depending on the resistance mechanisms involved.

Characterization and Potentiating Effects of the Ethanolic Extracts of the Red Seaweed Gracillaria sp. on the Activity of Carbenicillin against Vibrios

β-lactam-resistant Vibrio strains are a significant clinical problem, and β-lactamase inhibitors are generally coadministered with β-lactam drugs to control drug-resistant bacteria. Seaweed is a rich source of natural bioactive compounds; however, their potential as β-lactamase inhibitors against bacterial pathogens remains unknown. Herein, we evaluated the potential β-lactamase inhibitory effect of the ethanolic extracts of the red seaweed Gracilaria sp. (GE) against four Vibrio strains. The minimum inhibitory concentration, half-maximal inhibitory concentration, checkerboard assay results, and time-kill study results indicate that GE has limited antibacterial activity but can potentiate the activity of the β-lactam antibiotic carbenicillin against Vibrio parahemolyticus and V. cholerae. We overexpressed and purified recombinant metallo-β-lactamase, VarG, from V. cholerae for in vitro studies and observed that adding GE reduced the carbenicillin and nitrocefin degradation by VarG by 20% and 60%, respectively. Angiotensin I-converting enzyme inhibition studies demonstrated that GE did not inhibit VarG via metal chelation. Toxicity assays indicated that GE exhibited mild toxicity against human cells. Through gas chromatography and mass spectrometry, we showed that GE comprises alkaloids, phenolic compounds, terpenoids, terpenes, and halogenated aromatic compounds. This study revealed that extracts of the red seaweed Gracillaria sp. can potentially inhibit β-lactamase activity.

Increased zinc levels facilitate phenotypic detection of ceftazidime-avibactam resistance in metallo-β-lactamase-producing Gram-negative bacteria

Ceftazidime-avibactam is one of the last resort antimicrobial agents for the treatment of carbapenem-resistant, Gram-negative bacteria. Metallo-β-lactamase-producing bacteria are considered to be ceftazidime-avibactam resistant. Here, we evaluated a semi-automated antimicrobial susceptibility testing system regarding its capability to detect phenotypic ceftazidime-avibactam resistance in 176 carbapenem-resistant, metallo-β-lactamase-producing Enterobacterales and Pseudomonas aeruginosa isolates. Nine clinical isolates displayed ceftazidime-avibactam susceptibility in the semi-automated system and six of these isolates were susceptible by broth microdilution, too. In all nine isolates, metallo-β-lactamase-mediated hydrolytic activity was demonstrated with the EDTA-modified carbapenemase inactivation method. As zinc is known to be an important co-factor for metallo-β-lactamase activity, test media of the semi-automated antimicrobial susceptibility testing system and broth microdilution were supplemented with zinc. Thereby, the detection of phenotypic resistance was improved in the semi-automated system and in broth microdilution. Currently, ceftazidime-avibactam is not approved as treatment option for infections by metallo-β-lactamase-producing, Gram-negative bacteria. In infections caused by carbapenem-resistant Gram-negatives, we therefore recommend to rule out the presence of metallo-β-lactamases with additional methods before initiating ceftazidime-avibactam treatment.

Resistance to aztreonam-avibactam due to CTX-M-15 in the presence of penicillin-binding protein 3 with extra amino acids in Escherichia coli

Aztreonam-avibactam is a promising combination to treat carbapenem-resistant Enterobacterales including coverage for metallo-β-lactamases. Escherichia coli strains resistant to aztreonam-avibactam have emerged but resistance mechanisms remain to be elucidated. We performed a study to investigate the mechanism for aztreonam-avibactam in a carbapenem-resistant Escherichia coli clinical strain. This strain was resistant to aztreonam-avibactam (aztreonam MIC, 16 mg/L in the presence of 4 mg/L avibactam). Whole genome sequencing revealed that the strain carried metallo-β-lactamase gene bla_NDM-4 and the extended-spectrum β-lactamase (ESBL) gene bla_CTX-M-15 and had a YRIK four amino acid insertion in penicillin-binding protein 3 (PBP3). bla_CTX-M-15 was cloned into pET-28a(+), followed by the transformation, with the gene, of E. coli strain 035125∆pCMY42 possessing the YRIK insertion in PBP3 and strain BL21 with the wildtype PBP3. bla_CTX-M-14, another common ESBL gene, and bla_CTX-M-199, a hybrid of bla_CTX-M-14 and bla_CTX-M-15 were also individually cloned into both E. coli strains for comparison. Aztreonam-avibactam resistance was only observed in the E. coli strains with the YRIK insertion in PBP3 that produced CTX-M-15 or its hybrid enzyme CTX-M-199. Checkerboard titration assays were performed to determine the synergistic effects between aztreonam-avibactam and ceftazidime or meropenem. Doubling avibactam concentration in vitro reversed aztreonam-avibactam resistance, while the combination of aztreonam-avibactam and ceftazidime or meropenem did not. In conclusion, CTX-M enzymes with activity against aztreonam, (e.g., CTX-M-15 and CTX-M-199), can confer resistance in the combination of PBP3 with YRIK insertions in metallo-β-lactamase-producing carbapenem-resistant E. coli. Doubling the concentration of avibactam may overcome such resistance.

Klebsiella pneumoniae Carbapenemase Variants Resistant to Ceftazidime-Avibactam: an Evolutionary Overview

First variants of the Klebsiella pneumoniae carbapenemase (KPC), KPC-2 and KPC-3, have encountered a worldwide success, particularly in K. pneumoniae isolates. These beta-lactamases conferred resistance to most beta-lactams including carbapenems but remained susceptible to new beta-lactam/beta-lactamase inhibitors, such as ceftazidime-avibactam. After the marketing of ceftazidime-avibactam, numerous variants of KPC resistant to this association have been described among isolates recovered from clinical samples or derived from experimental studies. In KPC variants resistant to ceftazidime-avibactam, point mutations, insertions and/or deletions have been described in various hot spots. Deciphering the impact of these mutations is crucial, not only from a therapeutic point of view, but also to follow the evolution in time and space of KPC variants resistant to ceftazidime-avibactam. In this review, we describe the mutational landscape of the KPC beta-lactamase toward ceftazidime-avibactam resistance based on a multidisciplinary approach including epidemiology, microbiology, enzymology, and thermodynamics. We show that resistance is associated with three hot spots, with a high representation of insertions and deletions compared with other class A beta-lactamases. Moreover, extension of resistance to ceftazidime-avibactam is associated with a trade-off in the resistance to other beta-lactams and a decrease in enzyme stability. Nevertheless, the high natural stability of KPC could underlay the propensity of this enzyme to acquire in vivo mutations conferring resistance to ceftazidime-avibactam (CAZavi), particularly via insertions and deletions.

OXA-48-Like β-Lactamases: Global Epidemiology, Treatment Options, and Development Pipeline

Modern medicine is threatened by the rising tide of antimicrobial resistance, especially among Gram-negative bacteria, where resistance to β-lactams is most often mediated by β-lactamases. The penicillin and cephalosporin ascendancies were, in their turn, ended by the proliferation of TEM penicillinases and CTX-M extended-spectrum β-lactamases. These class A β-lactamases have long been considered the most important. For carbapenems, however, the threat is increasingly from the insidious rise of a class D carbapenemase, OXA-48, and its close relatives. Over the past 20 years, OXA-48 and "OXA-48-like" enzymes have proliferated to become the most prevalent enterobacterial carbapenemases across much of Europe, Northern Africa, and the Middle East. OXA-48-like enzymes are notoriously difficult to detect because they often cause only low-level in vitro resistance to carbapenems, meaning that the true burden is likely underestimated. Despite this, they are associated with carbapenem treatment failures. A highly conserved incompatibility complex IncL plasmid scaffold often carries bla_OXA-48 and may carry other antimicrobial resistance genes, leaving limited treatment options. High conjugation efficiency means that this plasmid is sometimes carried by multiple Enterobacterales in a single patient. Producers evade most β-lactam-β-lactamase inhibitor combinations, though promising agents have recently been licensed, notably ceftazidime-avibactam and cefiderocol. The molecular machinery enabling global spread, current treatment options, and the development pipeline of potential new therapies for Enterobacterales that produce OXA-48-like β-lactamases form the focus of this review.

Aztreonam-avibactam may not replace ceftazidime/avibactam: the case of KPC-21 carbapenemase and penicillin-binding protein 3 with four extra amino acids

Aztreonam/avibactam is a promising antimicrobial combination with additional coverage for metallo-β-lactamases compared with ceftazidime/avibactam. A carbapenem-resistant bla_KPC-2-carrying Escherichia coli clinical isolate had four extra amino acids in penicillin-binding protein 3 (PBP3), which has been known to mediate reduced susceptibility to aztreonam/avibactam. This prompted us to investigate whether the strain could develop resistance to aztreonam/avibactam after exposure to the combination. A mutant with high-level resistance to aztreonam/avibactam [minimum inhibitory concentration (MIC), 512/4 mg/L] was obtained after 5-day exposure to 0.5 × MIC but it remained susceptible to ceftazidime/avibactam (MIC, 4/4 mg/L). The mutant had a single nucleotide polymorphism (SNP) in bla_KPC-2 to encode KPC-21 with a Trp105Arg amino acid substitution. By cloning into E. coli BL21, bla_KPC-21 could mediate reduced susceptibility to aztreonam/avibactam (MIC, from ≤0.03/4 to 1/4 mg/L), which was still below the breakpoint to define resistance. In contrast, when bla_KPC-21 was cloned in E. coli 035125ΔpCMY42 with four extra amino acids in PBP3, which was generated in our previous work, the strain exhibited high-level resistance to aztreonam/avibactam (MIC, 256/4 mg/L). The above findings highlight that although aztreonam/avibactam has a broader spectrum than ceftazidime/avibactam, strains may develop resistance to the former combination but remain susceptible to the latter. The discrepancy is due to mutation of KPC-2 to KPC-21 in combination with the insertion of four extra amino acids in PBP3.

In vitro susceptibilities of isolates of potentially naturally inducible chromosomal AmpC-producing metallo-β-lactamase-negative carbapenem-resistant Enterobacterales species to ceftazidime-avibactam: Data from the Antimicrobial Testing Leadership and Surveillance Programme, 2012-2019

In total, 74,570 potentially naturally inducible chromosomal AmpC-producing (PNIC-AmpC) Enterobacterales isolates included in the Antimicrobial Testing Leadership and Surveillance Programme were obtained worldwide from 2012 to 2019 (22,503 from 2012 to 2014 and 52,067 from 2015 to 2019). One hundred seventeen and 711 isolates obtained in 2012-2014 and 2015-2019, respectively, were carbapenem-resistant Enterobacterales (PNIC-AmpC-CRE). The minimum inhibitory concentrations of ceftazidime-avibactam for these isolates against were determined using the broth microdilution method. Genes encoding different Ambler classes of β-lactamases were investigated using multiplex PCR. After 97 isolates harboring genes encoding metallo-β-lactamases (MβL) were excluded, 731 PNIC-AmpC MβL-negative CRE isolates (101 from 2012 to 2014 and 630 from 2015 to 2019) were included in this study. Enterobacter cloacae complex species, Escherichia coli, and Citrobacter freundii complex species accounted for 36.3% (n = 265), 30.4% (n = 222), and 11.8% (n = 86), respectively, followed by Providencia species (n = 72), Serratia species (n = 52), and Klebsiella aerogenes (n = 34). The resistance rates to ceftazidime-avibactam for the overall PNIC-AmpC MβL-negative CRE isolates differed markedly between the two periods (35.6% vs. 63.3%, P < 0.001). Similar trends were observed for the MβL-negative-CR-E. cloacae complex species (47.4% vs. 65.2%; P = 0.046) and MβL-negative-CR-E. coli (16.2% vs. 63.8%; P < 0.001) but not for MβL-negative-CR-C. freundii complex species (40% vs. 62%; P = 0.153). Amongst the PNIC-AmpC MβL-negative CRE isolates, resistance rates to ceftazidime-avibactam worsened. Caution should be taken when empirically prescribing ceftazidime-avibactam for infections caused by PNIC-AmpC-CRE before susceptibility data are available.

The primary pharmacology of ceftazidime/avibactam: in vitro translational biology

Previous reviews of ceftazidime/avibactam have focused on in vitro molecular enzymology and microbiology or the clinically associated properties of the combination. Here we take a different approach. We initiate a series of linked reviews that analyse research on the combination that built the primary pharmacology data required to support the clinical and business risk decisions to perform randomized controlled Phase 3 clinical trials, and the additional microbiological research that was added to the above, and the safety and chemical manufacturing and controls data, that constituted successful regulatory licensing applications for ceftazidime/avibactam in multiple countries, including the USA and the EU. The aim of the series is to provide both a source of reference for clinicians and microbiologists to be able to use ceftazidime/avibactam to its best advantage for patients, but also a case study of bringing a novel β-lactamase inhibitor (in combination with an established β-lactam) through the microbiological aspects of clinical development and regulatory applications, updated finally with a review of resistance occurring in patients under treatment. This first article reviews the biochemistry, structural biology and basic microbiology of the combination, showing that avibactam inhibits the great majority of serine-dependent β-lactamases in Enterobacterales and Pseudomonas aeruginosa to restore the in vitro antibacterial activity of ceftazidime. Translation to efficacy against infections in vivo is reviewed in the second co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac172).

The Role of Colistin in the Era of New β-Lactam/β-Lactamase Inhibitor Combinations

With the current crisis related to the emergence of carbapenem-resistant Gram-negative bacteria (CR-GNB), classical treatment approaches with so-called “old-fashion antibiotics” are generally unsatisfactory. Newly approved β-lactam/β-lactamase inhibitors (BLBLIs) should be considered as the first-line treatment options for carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. However, colistin can be prescribed for uncomplicated lower urinary tract infections caused by CR-GNB by relying on its pharmacokinetic and pharmacodynamic properties. Similarly, colistin can still be regarded as an alternative therapy for infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) until new and effective agents are approved. Using colistin in combination regimens (i.e., including at least two in vitro active agents) can be considered in CRAB infections, and CRE infections with high risk of mortality. In conclusion, new BLBLIs have largely replaced colistin for the treatment of CR-GNB infections. Nevertheless, colistin may be needed for the treatment of CRAB infections and in the setting where the new BLBLIs are currently unavailable. In addition, with the advent of rapid diagnostic methods and novel antimicrobials, the application of personalized medicine has gained significant importance in the treatment of CRE infections.

Epidemiology of resistance of carbapenemase-producing Klebsiella pneumoniae to ceftazidime-avibactam in a Chinese hospital

AIMS

Klebsiella pneumoniae has been reported to develop increased antibiotic resistance. Ceftazidime-avibactam (CZA) is a novel antibiotic with activity against serine-lactamase. Here, we investigated the sensitivity of carbapenem-resistant K. pneumoniae (CRKP) to CZA and the mechanisms of drug resistance in our hospital.

METHODS AND RESULTS

Patient characteristics were obtained from medical records. K. pneumoniae and its antibiotic susceptibility were determined using the Vitek-2 Compact instrument. The antibiotic resistance genes KPC, NDM, OXA-48, VIM, IMP, CIM, SPM, TMB, SMB, SIM, AIM and DIM were detected using real-time PCR. Multilocus sequence typing was used for genetic RELATEDNESS analysis. In total, 121 CRKP strains were isolated from patients in the intensive care unit (51·2%), senior ward (12·4%) and neurosurgery department (10%). With an average age of 72·5 years, most patients were in care for respiratory (34·7%), brain (20·7%), digestive tract (13·2%) and cardiovascular (8·3%) diseases. Specimens were predominantly obtained from sputum (39·67%), urine (29·75%) and blood (6·61%).

CONCLUSION

Of 23 CZA-resistant CRKP strains (19·01%), ST11 being the most common at 56·52%, 11 NDM-1-positive (47·83%) and four NDM-5-positive (17·39%) strains were detected.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study indicates that CZA resistance occurs in ~19·01% CRKP strains and that blaNDM-1 and blaNDM-5 might be critical for resistance.

In vitro activity of ceftazidime-avibactam against Enterobacterales and Pseudomonas aeruginosa isolates collected in Latin America as part of the ATLAS global surveillance program, 2017-2019

The Antimicrobial Testing Leadership and Surveillance (ATLAS) global surveillance program collected clinical isolates of Enterobacterales (n = 8416) and Pseudomonas aeruginosa (n = 2521) from 41 medical centers in 10 Latin American countries from 2017 to 2019. In vitro activities of ceftazidime-avibactam and comparators were determined using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. Overall, 98.1% of Enterobacterales and 86.9% of P. aeruginosa isolates were susceptible to ceftazidime-avibactam. When isolates were analyzed by country of origin, susceptibility to ceftazidime-avibactam for Enterobacterales ranged from 97.8% to 100% for nine of 10 countries (except Guatemala, 86.3% susceptible) and from 75.9% to 98.4% for P. aeruginosa in all 10 countries. For Enterobacterales, 100% of AmpC-positive, ESBL- and AmpC-positive, GES-type carbapenemase-positive, and OXA-48-like-positive isolates were ceftazidime-avibactam-susceptible as were 99.8%, 91.8%, and 74.7% of ESBL-positive, multidrug-resistant (MDR), and meropenem-nonsusceptible isolates. Among meropenem-nonsusceptible isolates of Enterobacterales, 24.4% (139/570) carried a metallo-β-lactamase (MBL); 83.3% of the remaining meropenem-nonsusceptible isolates carried another class of carbapenemase and 99.4% of those isolates were ceftazidime-avibactam-susceptible. Among meropenem-non-susceptible isolates of P. aeruginosa (n = 835), 25.6% carried MBLs; no acquired β-lactamase was identified in the majority of isolates (64.8%; 87.2% of those isolates were ceftazidime-avibactam-susceptible). Overall, clinical isolates of Enterobacterales collected in Latin America from 2017 to 2019 were highly susceptible to ceftazidime-avibactam, including isolates carrying ESBLs, AmpCs, and KPCs. Country-specific variation in susceptibility to ceftazidime-avibactam was more common among isolates of P. aeruginosa than Enterobacterales. The frequency of MBL-producers among Enterobacterales from Latin America was low (1.7% of all isolates; 146/8,416), but higher than reported in previous surveillance studies.

Selection and characterization of mutational resistance to aztreonam/avibactam in β-lactamase-producing Enterobacterales

BACKGROUND

Aztreonam/avibactam is being developed for its broad activity against carbapenemase-producing Enterobacterales, including those with metallo-β-lactamases (MBLs). Its potential to select resistance in target pathogens was explored. Findings are compared with previous data for ceftazidime/avibactam and ceftaroline/avibactam.

METHODS

Single-step mutants were sought from 52 Enterobacterales with AmpC, ESBL, KPC, MBL and OXA-48-like enzymes. Mutation frequencies were calculated. MICs were determined by CLSI agar dilution. Genomes were sequenced using Illumina methodology.

RESULTS

Irrespective of β-lactamase type and of whether avibactam was used at 1 or 4 mg/L, mutants could rarely be obtained at >4× the starting MIC, and most MIC rises were correspondingly small. Putative resistance (MIC >8 + 4 mg/L) associated with changes to β-lactamases was seen only for mutants of AmpC, where it was associated with Asn346Tyr and Tyr150Cys substitutions. Asn346Tyr led to broad resistance to avibactam combinations; Tyr150Cys significantly affected only aztreonam/avibactam. MIC rises up to 4 + 4 mg/L were seen for producers of mutant KPC-2 or -3 enzymes, and were associated with Trp105Arg, Ser106Pro and Ser109Pro substitutions, which all reduced the MICs of other β-lactams. For producers of other β-lactamase types, we largely found mutants with lesions in baeRS or envZ, putatively affecting drug accumulation. Single mutants had lesions in ampD, affecting AmpC expression or ftsI, encoding PBP3.

CONCLUSIONS

The risk of mutational resistance to aztreonam/avibactam appears smaller than for ceftazidime/avibactam, where Asp179Tyr arises readily in KPC enzymes, conferring frank resistance. Asn346 substitutions in AmpC enzymes may remain a risk, having been repeatedly selected with multiple avibactam combinations in vitro.

The Revival of Aztreonam in Combination with Avibactam against Metallo-β-Lactamase-Producing Gram-Negatives: A Systematic Review of In Vitro Studies and Clinical Cases

Infections caused by metallo-β-lactamase (MBL)-producing Enterobacterales and Pseudomonas are increasingly reported worldwide and are usually associated with high mortality rates (>30%). Neither standard therapy nor consensus for the management of these infections exist. Aztreonam, an old β-lactam antibiotic, is not hydrolyzed by MBLs. However, since many MBL-producing strains co-produce enzymes that could hydrolyze aztreonam (e.g., AmpC, ESBL), a robust β-lactamase inhibitor such as avibactam could be given as a partner drug. We performed a systematic review including 35 in vitro and 18 in vivo studies on the combination aztreonam + avibactam for infections sustained by MBL-producing Gram-negatives. In vitro data on 2209 Gram-negatives were available, showing the high antimicrobial activity of aztreonam (MIC ≤ 4 mg/L when combined with avibactam) in 80% of MBL-producing Enterobacterales, 85% of Stenotrophomonas and 6% of MBL-producing Pseudomonas. Clinical data were available for 94 patients: 83% of them had bloodstream infections. Clinical resolution within 30 days was reported in 80% of infected patients. Analyzing only patients with bloodstream infections (64 patients), death occurred in 19% of patients treated with aztreonam + ceftazidime/avibactam. The combination aztreonam + avibactam appears to be a promising option against MBL-producing bacteria (especially Enterobacterales, much less for Pseudomonas) while waiting for new antimicrobials.

Inhibitors of β-Lactamases. New Life of β-Lactam Antibiotics

β-Lactam antibiotics account for about 60% of all produced antibiotics. Due to a high activity and minimal side effects, they are the most commonly used class of antibacterial drugs for the treatment of various infectious diseases of humans and animals, including severe hospital infections. However, the emergence of bacteria resistant to β-lactams has led to the clinical inefficiency of these antibiotics, and as a result, their use in medicine has been limited. The search for new effective ways for overcoming the resistance to β-lactam antibiotics is an essential task. The major mechanism of bacterial resistance is the synthesis of β-lactamases (BLs) that break the antibiotic β-lactam ring. Here, we review specific inhibitors of serine β-lactamases and metallo-β-lactamases and discuss approaches for creating new inhibitors that would prolong the "life" of β-lactams.

Activity of β-lactam/taniborbactam (VNRX-5133) combinations against carbapenem-resistant Gram-negative bacteria

BACKGROUND

Boronates are of growing interest as β-lactamase inhibitors. The only marketed analogue, vaborbactam, principally targets KPC carbapenemases, but taniborbactam (VNRX-5133, Venatorx) has a broader spectrum.

METHODS

MICs of cefepime and meropenem were determined combined with taniborbactam or avibactam for carbapenem-resistant UK isolates. β-Lactamase genes and porin alterations were sought by PCR or sequencing.

RESULTS

Taniborbactam potentiated partner β-lactams against: (i) Enterobacterales with KPC, other class A, OXA-48-like, VIM and NDM (not IMP) carbapenemases; and (ii) Enterobacterales inferred to have combinations of ESBL or AmpC activity and impermeability. Potentiation of cefepime (the partner for clinical development) by taniborbactam was slightly weaker than by avibactam for Enterobacterales with KPC or OXA-48-like carbapenemases, but MICs of cefepime/taniborbactam were similar to those of ceftazidime/avibactam, and the spectrum was wider. MICs of cefepime/taniborbactam nonetheless remained >8 + 4 mg/L for 22%-32% of NDM-producing Enterobacterales. Correlates of raised cefepime/taniborbactam MICs among these NDM Enterobacterales were a cefepime MIC >128 mg/L, particular STs and, for Escherichia coli only: (i) the particular blaNDM variant (even though published data suggest all variants are inhibited similarly); (ii) inserts in PBP3; and (iii) raised aztreonam/avibactam MICs. Little or no potentiation of cefepime or meropenem was seen for Pseudomonas aeruginosa and Acinetobacter baumannii with MBLs, probably reflecting slower uptake or stronger efflux. Potentiation of cefepime was seen for Stenotrophomonas maltophilia and Elizabethkingia meningoseptica, which have both chromosomal ESBLs and MBLs.

CONCLUSIONS

Taniborbactam broadly reversed cefepime or meropenem non-susceptibility in Enterobacterales and, less reliably, in non-fermenters.

Pharmacokinetics and safety of aztreonam/avibactam for the treatment of complicated intra-abdominal infections in hospitalized adults: results from the REJUVENATE study

Objectives

To investigate pharmacokinetics (PK) and safety (primary objectives) and efficacy (secondary objective) of the investigational monobactam/β-lactamase inhibitor combination aztreonam/avibactam in patients with complicated intra-abdominal infection (cIAI).

Methods

This Phase 2a open-label, multicentre study (NCT02655419; EudraCT 2015-002726-39) enrolled adults with cIAI into sequential cohorts for 5–14 days treatment. Cohort 1 patients received an aztreonam/avibactam loading dose of 500/137 mg (30 min infusion), followed by maintenance doses of 1500/410 mg (3 h infusions) q6h; Cohort 2 received 500/167 mg (30 min infusion), followed by 1500/500 mg (3 h infusions) q6h. Cohort 3 was an extension of exposure at the higher dose regimen. Doses were adjusted for creatinine clearance of 31–50 mL/min (Cohorts 2 + 3). All patients received IV metronidazole 500 mg q8h. PK, safety and efficacy were assessed.

Results

Thirty-four patients (Cohort 1, n = 16; Cohorts 2 + 3, n = 18) comprised the modified ITT (MITT) population. Mean exposures of aztreonam and avibactam in Cohorts 2 + 3 were consistent with those predicted to achieve joint PK/pharmacodynamic target attainment in >90% patients. Adverse events (AEs) were similar between cohorts. The most common AEs were hepatic enzyme increases [n = 9 (26.5%)] and diarrhoea [n = 5 (14.7%)]. Clinical cure rates at the test-of-cure visit overall were 20/34 (58.8%) (MITT) and 14/23 (60.9%) (microbiological-MITT population).

Conclusions

Observed AEs were consistent with the known safety profile of aztreonam monotherapy, with no new safety concerns identified. These data support selection of the aztreonam/avibactam 500/167 mg (30 min infusion) loading dose and 1500/500 mg (3 h infusions) maintenance dose q6h regimen, in patients with creatinine clearance >50 mL/min, for the Phase 3 development programme.

In vitro activity of ceftazidime/avibactam against isolates of carbapenem-non-susceptible Enterobacteriaceae collected during the INFORM global surveillance programme (2015-17)

Objectives

To report data for ceftazidime/avibactam and comparators against meropenem-non-susceptible Enterobacteriaceae collected globally (excluding centres in the USA) from 2015 to 2017 as part of the International Network For Optimal Resistance Monitoring (INFORM) surveillance programme.

Methods

MICs and susceptibility were determined using EUCAST broth microdilution methodology and EUCAST breakpoints. Isolates were screened to detect genes encoding β-lactamases using multiplex PCR assays. MBL-positive isolates were those in which one or more of the IMP, VIM and/or NDM genes were detected.

Results

A total of 1460 meropenem-non-susceptible isolates were collected and, of the agents on the panel, susceptibility was highest to ceftazidime/avibactam, colistin and tigecycline [73.0%, 77.0% (1081/1403) and 78.1%, respectively]. Ceftazidime/avibactam was not active against MBL-positive isolates (n=367); these isolates showed the highest rates of susceptibility to colistin (92.1%, 303/329), tigecycline (71.9%) and amikacin (46.6%). A total of 394 isolates were resistant to ceftazidime/avibactam and, of the 369 isolates that were screened, 98.4% were found to carry a gene encoding an MBL enzyme. Among isolates that were identified as carbapenemase positive and MBL negative (n=910), susceptibility was highest to ceftazidime/avibactam (99.8%). Susceptibility was also highest to ceftazidime/avibactam among isolates that were carbapenemase negative and MBL negative (94/98, 95.9%).

Conclusions

These data highlight the need for continued surveillance of antimicrobial activity as well as the need for new antimicrobials to treat infections caused by meropenem-non-susceptible Enterobacteriaceae, for which the options are extremely limited.

Carbapenem-Resistant Enterobacterales, Carbapenem Resistant Organisms, Carbapenemase-Producing Enterobacterales, and Carbapenemase-Producing Organisms: Terminology Past its "Sell-By Date" in an Era of New Antibiotics and Regional Carbapenemase Epidemiology

Carbapenem resistance in Gram-negative bacteria is a public health concern. Consequently, numerous government and agency reports discuss carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant organisms (CROs). Unfortunately, these terms are fuzzy. Do they include (1) Proteeae with inherent imipenem resistance; (2) porin-deficient Enterobacterales resistant to ertapenem but not other carbapenems; (3) Enterobacterales with OXA-48-like enzymes that remain "carbapenem susceptible" at breakpoint; and (4) Pseudomonas aeruginosa that merely lack porin OprD? Counting CPE or CPOs is better but still insufficient, because different carbapenemases have differing treatment implications, particularly for new β-lactam/β-lactamase inhibitor combinations. At the least, it is essential for authors, journals, and regulatory agencies to specify the carbapenemases meant. The future may demand even greater precision, for mutations can alter hydrolytic activity, and the ability to confer resistance, within carbapenemase families.

In vitro Effect of the Combination of Aztreonam and Amoxicillin/Clavulanic Acid Against Carbapenem-Resistant Gram-Negative Organisms Producing Metallo-β-Lactamase

INTRODUCTION

Antibiotics for treating infectious diseases caused by carbapenem-resistant Gram-negative pathogens (CR-GNOs) are very limited in clinical practice. We aim to provide supportive evidence by revealing the combined effect of aztreonam (ATM) and amoxicillin/clavulanic acid (AMC) against GNOs with carbapenem resistance mediated by metallo-β-lactamase (MBL).

METHODS

All isolates were identified by the VITEK system and EDTA inhibitory assays. PCR followed by sequencing was conducted to confirm the genotypes of MBL and extended spectrum β-lactamase (ESBL). Time kill assay was performed to clarify the bactericidal effect of drug combination.

RESULTS

A total of 59 MBL-producing CR-GNOs (33 Enterobacteriaceae spp. isolates and 26 Pseudomonadales isolates) were identified and there found three MBL genes, namely, bla IMP, bla NDM and bla VIM, with ratios of 76.2%, 11.8% and 11.8%, respectively. The Enterobacteriaceae spp. isolates were commonly positive for the ESBL genes, including bla TEM (18 isolates), bla SHV (20 isolates) and bla CTX-M-1 (8 isolates), while the P. aeruginosa isolates were positive for bla OXA-10 (11 isolates). The checkerboard microdilution assay was used to detect combination effect of ATM and AMC, which showed synergy (97.0%) and partial synergy (3.0%) in Enterobacteriaceae spp. isolates, and partial synergy (42.3%) and indifference (34.6%) in the Pseudomonadales isolates. Four Enterobacteriaceae spp. isolates were selected for a time-kill assay, and rapid bactericidal effects were observed in the combination groups compared to the control and mono-ATM groups; these effects began in the first hour and continued to the sixth hour, yielding a 5- to 7-fold reduction in Log10 CFU/mL.

DISCUSSION

The combination of ATM and AMC would be an available option to control infections caused by MBL-producing CR-GNOs, especially Enterobacteriaceae spp. isolates that coproduce ESBLs, and exhibit significant synergic effects in vitro.

In Vitro Activities and Inoculum Effects of Ceftazidime-Avibactam and Aztreonam-Avibactam against Carbapenem-Resistant Enterobacterales Isolates from South Korea

Ceftazidime-avibactam (CAZ-AVI) and aztreonam-avibactam (AZT-AVI) are novel antibiotic combinations active against multidrug-resistant Gram-negative pathogens. This study aimed to evaluate their in vitro activities and inoculum effects in carbapenem-resistant Enterobacterales (CRE), including carbapenemase-producing (CP)-CRE and non-CP-CRE. A total of 81 independent clinical isolates of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae were collected. CAZ-AVI and AZT-AVI minimal inhibitory concentrations (MICs) were evaluated by broth microdilution using standard and high inocula. The inoculum effect was defined as an ≥8-fold increase in MIC with high inoculum. Phenotypic determination of β-lactam resistance mechanism and PCR for carbapenemase genes were performed. Of the 81 CRE isolates, 35 (43%) were CP-CRE. Overall, 73% of the isolates were susceptible to CAZ-AVI, and 95% had low AZT-AVI MICs (≤8 µg/mL). The MIC_50/MIC₉₀s of CAZ-AVI and AZT-AVI were 4/≥512 µg/mL and 0.5/4 µg/mL, respectively. CAZ-AVI was more active against non-CP-CRE than against CP-CRE (susceptibility 80% vs. 63%, p = 0.08; MIC₅₀/MIC₉₀, 2/16 μg/mL vs. 4/≥512 μg/mL), whereas AZT-AVI was more active against CP-CRE (MIC₅₀/MIC₉₀, 0.25/1 μg/mL vs. 0.5/8 μg/mL). All four isolates with high AZT-AVI MIC (≥16 μg/mL) were resistant to CAZ-AVI, but only 18% (4/22) of CAZ-AVI-resistant isolates had high AZT-AVI MIC. The rates of the inoculum effect for CAZ-AVI and AZT-AVI were 18% and 47%, respectively (p < 0.001). Interestingly, the frequency of the AZT-AVI inoculum effect was higher in K. pneumoniae than E. coli (64% vs. 8%, p < 0.001). AZT-AVI is more active against CRE than CAZ-AVI, even in CP-CRE and CAZ-AVI-resistant isolates. The presence of a substantial inoculum effect may contribute to clinical failure in high-inoculum infections treated with AZT-AVI.

In Vitro Activity of Cefiderocol, a Siderophore Cephalosporin, against Multidrug-Resistant Gram-Negative Bacteria

Cefiderocol is a parenteral siderophore cephalosporin with a catechol-containing 3' substituent. We evaluated its MICs against Gram-negative bacteria, using iron-depleted Mueller-Hinton broth. The panel comprised 305 isolates of Enterobacterales, 111 of Pseudomonas aeruginosa, and 99 of Acinetobacter baumannii, all selected for carbapenem resistance and multidrug resistance to other agents. At 2 and 4 μg/ml, cefiderocol inhibited 78.7 and 92.1%, respectively, of all Enterobacterales isolates tested, with rates of 80 to 100% for isolates with all modes of carbapenem resistance except NDM enzymes (41.0% inhibited at 2 μg/ml and 72.1% at 4 μg/ml) or combinations of extended-spectrum β-lactamase (ESBL) and porin loss (61.5% inhibited at 2 μg/ml and 88.5% at 4 μg/ml). Cefiderocol also inhibited 81.1 and 86.5% of all P. aeruginosa isolates at 2 and 4 μg/ml, respectively, with rates of 80 to 100% for isolates with VIM, IMP, GES, or VEB β-lactamases and slightly lower rates for those with NDM (45.5% at 2 μg/ml and 72.7% at 4 μg/ml) and PER (66.7% at 2 μg/ml and 73.3% at 4 μg/ml) enzymes; 63.3% of P. aeruginosa isolates were inhibited at the FDA's 1-μg/ml breakpoint. Lastly, cefiderocol at 2 and 4 μg/ml inhibited 80.8 and 88.9% of the A. baumannii isolates, respectively, with rates of >85% for isolates with OXA-51-like, -23, -24, or -58 enzymes and 50% at 2 μg/ml and 80% at 4 μg/ml for those with NDM carbapenemases. Dipicolinic acid and avibactam weakly potentiated cefiderocol against Enterobacterales isolates with metallo-β-lactamases (MBLs) and serine carbapenemase, respectively, indicating incomplete β-lactamase stability.

Struggle To Survive: the Choir of Target Alteration, Hydrolyzing Enzyme, and Plasmid Expression as a Novel Aztreonam-Avibactam Resistance Mechanism

Aztreonam-avibactam is a promising antimicrobial combination against multidrug-resistant organisms, such as carbapenemase-producing Enterobacterales Resistance to aztreonam-avibactam has been found, but the resistance mechanism remains poorly studied. We recovered three Escherichia coli isolates of an almost identical genome but exhibiting varied aztreonam-avibactam resistance. The isolates carried a cephalosporinase gene, bla _CMY-42, on IncIγ plasmids with a single-nucleotide variation in an antisense RNA-encoding gene, inc, of the replicon. The isolates also had four extra amino acids (YRIK) in penicillin-binding protein 3 (PBP3) due to a duplication of a 12-nucleotide (TATCGAATTAAC) stretch in pbp3 By cloning and plasmid-curing experiments, we found that elevated CMY-42 cephalosporinase production or amino acid insertions in PBP3 alone mediated slightly reduced susceptibility to aztreonam-avibactam, but their combination conferred aztreonam-avibactam resistance. We show that the elevated CMY-42 production results from increased plasmid copy numbers due to mutations in inc We also verified the findings using in vitro mutation assays, in which aztreonam-avibactam-resistant mutants also had mutations in inc and elevated CMY-42 production compared with the parental strain. This choir of target modification, hydrolyzing enzyme, and plasmid expression represents a novel, coordinated, complex antimicrobial resistance mechanism and also reflects the struggle of bacteria to survive under selection pressure imposed by antimicrobial agents.IMPORTANCE Carbapenemase-producing Enterobacterales (CPE) is a serious global challenge with limited therapeutic options. Aztreonam-avibactam is a promising antimicrobial combination with activity against CPE producing serine-based carbapenemases and metallo-β-lactamases and has the potential to be a major option for combatting CPE. Aztreonam-avibactam resistance has been found, but resistance mechanisms remain largely unknown. Understanding resistance mechanisms is essential for optimizing treatment and developing alternative therapies. Here, we found that either penicillin-binding protein 3 modification or the elevated expression of cephalosporinase CMY-42 due to increased plasmid copy numbers does not confer resistance to aztreonam-avibactam, but their combination does. We demonstrate that increased plasmid copy numbers result from mutations in antisense RNA-encoding inc of the IncIγ replicon. The findings reveal that antimicrobial resistance may be due to concerted combinatorial effects of target alteration, hydrolyzing enzyme, and plasmid expression and also highlight that resistance to any antimicrobial combination will inevitably emerge.

Metallo-β-Lactamases: Structure, Function, Epidemiology, Treatment Options, and the Development Pipeline

Modern medicine is threatened by the global rise of antibiotic resistance, especially among Gram-negative bacteria. Metallo-β-lactamase (MBL) enzymes are a particular concern and are increasingly disseminated worldwide, though particularly in Asia. Many MBL producers have multiple further drug resistances, leaving few obvious treatment options. Nonetheless, and more encouragingly, MBLs may be less effective agents of carbapenem resistance in vivo, under zinc limitation, than in vitro Owing to their unique structure and function and their diversity, MBLs pose a particular challenge for drug development. They evade all recently licensed β-lactam-β-lactamase inhibitor combinations, although several stable agents and inhibitor combinations are at various stages in the development pipeline. These potential therapies, along with the epidemiology of producers and current treatment options, are the focus of this review.

Dramatic rise in the proportion of ESBL-producing Escherichia coli and Klebsiella pneumoniae among clinical isolates identified in Canadian hospital laboratories from 2007 to 2016

OBJECTIVES

To assess the prevalence, antimicrobial susceptibilities and molecular characteristics of ESBL-producing Escherichia coli and Klebsiella pneumoniae infecting patients receiving care in Canadian hospitals from January 2007 to December 2016.

METHODS

Clinical isolates of E. coli (n = 8387) and K. pneumoniae (n = 2623) submitted to CANWARD, an ongoing Canadian national surveillance study, were tested using the CLSI reference broth microdilution method to determine their susceptibility to 15 antimicrobial agents. ESBL-producing E. coli and K. pneumoniae confirmed by the CLSI phenotypic method and putative AmpC-producing E. coli underwent PCR testing and DNA sequencing to identify resistance genes. Annual proportions of isolates harbouring ESBL and AmpC genes were assessed by the Cochran-Armitage test of trend.

RESULTS

The annual proportion of isolates of E. coli that were ESBL producing increased from 3.4% in 2007 to 11.1% in 2016 (P < 0.0001); >95% of ESBL-producing E. coli were susceptible to amikacin, colistin, ertapenem, meropenem and tigecycline. The proportion of isolates of K. pneumoniae that were ESBL producing increased from 1.3% in 2007 to 9.7% in 2016 (P < 0.0001); >95% of ESBL-producing K. pneumoniae were susceptible to amikacin and meropenem. CTX-M-15 was the predominant genotype in both ESBL-producing E. coli (64.2% of isolates) and ESBL-producing K. pneumoniae (51.0%). The annual proportion of isolates of E. coli that were AmpC producing [annual proportion mean 1.9% (range 0.3%-3.1%)] was unchanged from 2007 to 2016 (P > 0.5).

CONCLUSIONS

The prevalence of both ESBL-producing E. coli and K. pneumoniae increased significantly in Canada during the study period while the prevalence of AmpC-producing E. coli remained low and stable.

In vitro activity of ceftazidime/avibactam and comparators against Gram-negative bacterial isolates collected from Latin American centres between 2015 and 2017

Objectives

We report the in vitro activity of ceftazidime/avibactam and comparators against 7729 Enterobacterales isolates and 2053 Pseudomonas aeruginosa isolates collected from six Latin American countries between 2015 and 2017.

Methods

A central reference laboratory performed antimicrobial susceptibility testing using broth microdilution panels according to CLSI guidelines. The presence of β-lactamases was confirmed using multiplex PCR assays.

Results

Susceptibility rates among Enterobacterales were highest for ceftazidime/avibactam (99.3%, MIC₉₀ = 0.5 mg/L), meropenem (95.4%, MIC₉₀ = 0.12 mg/L) and amikacin (93.5%, MIC₉₀ = 8 mg/L). High susceptibility rates were observed for ceftazidime/avibactam in all six countries. The majority of carbapenemase-positive isolates among Enterobacterales (N = 366, 4.7%) were susceptible to ceftazidime/avibactam (86.9%), colistin (76.8%) and amikacin (60.9%); MBL-positive isolates (N = 49, 0.6%) were susceptible only to colistin (79.6%), with a minority susceptible to amikacin (49.0%), aztreonam and levofloxacin (both 30.6%). Highest rates of susceptibility among P. aeruginosa isolates were for colistin (99.2%) and ceftazidime/avibactam (86.6%), with rates of susceptibility to all other agents being <80.0%. MDR P. aeruginosa isolates (N = 712, 34.7%) had a high rate of susceptibility to colistin (98.9%); the rate of susceptibility to ceftazidime/avibactam was 61.4% and <50.0% to all other comparator agents. A total of 235 (11.4%) isolates of P. aeruginosa were carbapenemase positive and 148 (7.2%) were MBL positive; both subsets had high rates of susceptibility to colistin (98.3% and 100%, respectively).

Conclusions

Ceftazidime/avibactam susceptibility rates in Latin American countries are stable and high; ceftazidime/avibactam can be an appropriate treatment for patients with infections caused by Enterobacterales or P. aeruginosa and for whom treatment options may be limited.

Drugs for Gram-Negative Bugs From 2010-2019: A Decade in Review

A literature review spanning January 1, 2010, to December 31, 2019, was conducted using the PubMed and ISI Web of Science databases to determine the breadth of publication activity in the area of gram-negative bacteria antimicrobial therapy. The number of articles was used as a reflection of scholarly activity. First, PubMed was searched using the following Medical Subject Headings (MeSH): antibacterial agents, Enterobacteriaceae, Acinetobacter, and Pseudomonas. A total of 12 643 articles were identified within PubMed, and 77 862 articles were identified within ISI Web of Science that included these terms. Second, these articles were categorized by antibiotic class to identify relative contributions to the literature by drug category. Third, these studies were used to identify key trends in the treatment of gram-negative bacterial infections from the past decade. This review highlights advances made in the past 10 years in antibacterial pharmacotherapy and some of the challenges that await the next decade of practice.

Activity of nacubactam (RG6080/OP0595) combinations against MBL-producing Enterobacteriaceae

BACKGROUND

Diazabicyclooctanes (DBOs) are promising β-lactamase inhibitors. Some, including nacubactam (OP0595/RG6080), also bind PBP2 and have an enhancer effect, allowing activity against Enterobacteriaceae with MBLs, which DBOs do not inhibit. We tested the activity of nacubactam/β-lactam combinations against MBL-producing Enterobacteriaceae.

METHODS

Test panels comprised (i) 210 consecutive Enterobacteriaceae with NDM or VIM MBLs, as referred by UK diagnostic laboratories, and (ii) 99 supplementary MBL-producing Enterobacteriaceae, representing less prevalent phenotypes, species and enzymes. MICs were determined by CLSI agar dilution.

RESULTS

MICs of nacubactam alone were bimodal, clustering at 1-8 mg/L or >32 mg/L; >85% of values for Escherichia coli and Enterobacter spp. fell into the low MIC cluster, whereas Proteeae were universally resistant and the Klebsiella spp. were divided between the two groups. Depending on the prospective breakpoint (4 + 4 or 8 + 4 mg/L), and on whether all isolates were considered or solely the Consecutive Collection, meropenem/nacubactam and cefepime/nacubactam inhibited 80.3%-93.3% of MBL producers, with substantial gains over nacubactam alone. Against the most resistant isolates (comprising 57 organisms with MICs of nacubactam >32 mg/L, cefepime ≥128 mg/L and meropenem ≥128 mg/L), cefepime/nacubactam at 8 + 4 mg/L inhibited 63.2% and meropenem/nacubactam at 8 + 4 mg/L inhibited 43.9%. Aztreonam/nacubactam, incorporating an MBL-stable β-lactam partner, was almost universally active against the MBL producers and, unlike aztreonam/avibactam, had an enhancer effect.

CONCLUSIONS

Nacubactam combinations, including those using MBL-labile β-lactams, e.g. meropenem and cefepime, can overcome most MBL-mediated resistance. This behaviour reflects nacubactam's direct antibacterial and enhancer activity.

In vitro activity of aztreonam-avibactam against metallo-β-lactamase-producing Enterobacteriaceae-A multicenter study in China

OBJECTIVES

To study the molecular epidemiology of clinical metallo-β-lactamase (MBL)-producing Enterobacteriaceae isolates in China and to evaluate the antimicrobial susceptibility of MBL-Enterobacteriaceae isolates to aztreonam-avibactam.

METHODS

Bacterial speciation was determined using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PCR was used to screen for common carbapenemase genes. Antimicrobial susceptibility testing of common clinical antibiotics and aztreonam-avibactam was performed using the standard broth microdilution method.

RESULTS

A total of 161 MBL-Enterobacteriaceae isolates were included, with Klebsiella pneumoniae (n = 73, 45.4%) and Escherichia coli (n = 53, 32.9%) being the most common species. Among the 161 isolates, bla_NDM (n = 151), bla_IMP (n = 13), and bla_VIM (n = 2) were detected, including five strains (3.1%) co-harboring two MBLs. MBL-Enterobacteriaceae isolates frequently contained two (n = 55, 34.2%) or more (n = 89, 55.3%) additional serine β-lactamase genes (bla_KPC, bla_CTX-M, bla_TEM, or bla_SHV). Antimicrobial susceptibility testing showed that 81.4% of isolates (n = 131) were resistant to aztreonam. The rates of resistance to cefazolin, ceftazidime, ceftriaxone, cefotaxime, ampicillin-sulbactam, amoxicillin-clavulanic acid, and piperacillin-tazobactam were all over 90%. The addition of avibactam (4 μg/ml) significantly reduced the minimum inhibitory concentrations (MICs) of the aztreonam-resistant isolates by more than 8-fold (range ≤0.125 to 4 μg/ml), with a MIC₅₀/MIC₉₀ of ≤0.125/1 μg/ml among the 131 isolates. Overall, 96.9% (n = 156) of the total isolates were inhibited at an aztreonam-avibactam concentration of ≤1 μg/ml. Univariate and multivariate logistic regression analysis found that in patients with MBL-Enterobacteriaceae infections, the presence of pre-existing lung disease (adjusted odds ratio 8.267, 95% confidence interval 1.925-28.297; p = 0.004) was associated with a hazard effect on worse disease outcomes.

CONCLUSIONS

The combined use of aztreonam-avibactam is highly potent against MBL-Enterobacteriaceae and may serve as a new candidate for the treatment of infections caused by MBL-Enterobacteriaceae in China.

In Vitro Activity of Ceftazidime-Avibactam against Isolates from Respiratory and Blood Specimens from Patients with Nosocomial Pneumonia, Including Ventilator-Associated Pneumonia, in a Phase 3 Clinical Trial

Nosocomial pneumonia (NP), including ventilator-associated pneumonia (VAP), is increasingly associated with multidrug-resistant Gram-negative pathogens. This study describes the in vitro activity of ceftazidime-avibactam, ceftazidime, and relevant comparator agents against bacterial pathogens isolated from patients with NP, including VAP, enrolled in a ceftazidime-avibactam phase 3 trial. Gram-positive pathogens were included if coisolated with a Gram-negative pathogen. In vitro susceptibility was determined at a central laboratory using Clinical and Laboratory Standards Institute broth microdilution methods. Of 817 randomized patients, 457 (55.9%) had ≥1 Gram-negative bacterial pathogen(s) isolated at baseline, and 149 (18.2%) had ≥1 Gram-positive pathogen(s) coisolated. The most common isolated pathogens were Klebsiella pneumoniae (18.8%), Pseudomonas aeruginosa (15.8%), and Staphylococcus aureus (11.5%). Ceftazidime-avibactam was highly active in vitro against 370 isolates of Enterobacteriaceae, with 98.6% susceptible (MIC₉₀, 0.5 μg/ml) compared with 73.2% susceptible for ceftazidime (MIC₉₀, >64 μg/ml). The percent susceptibility values for ceftazidime-avibactam and ceftazidime against 129 P. aeruginosa isolates were 88.4% and 72.9% (MIC₉₀ values of 16 μg/ml and 64 μg/ml), respectively. Among ceftazidime-nonsusceptible Gram-negative isolates, ceftazidime-avibactam percent susceptibility values were 94.9% for 99 Enterobacteriaceae and 60.0% for 35 P. aeruginosa MIC₉₀ values for linezolid and vancomycin (permitted per protocol for Gram-positive coverage) were within their respective MIC susceptibility breakpoints against the Gram-positive pathogens isolated. This analysis demonstrates that ceftazidime-avibactam was active in vitro against the majority of Enterobacteriaceae and P. aeruginosa isolates from patients with NP, including VAP, in a phase 3 trial. (This study has been registered at ClinicalTrials.gov under identifier NCT01808092.).

Interplay between β-lactamases and new β-lactamase inhibitors

Resistance to β-lactam antibiotics in Gram-negative bacteria is commonly associated with production of β-lactamases, including extended-spectrum β-lactamases (ESBLs) and carbapenemases belonging to different molecular classes: those with a catalytically active serine and those with at least one active-site Zn²⁺ to facilitate hydrolysis. To counteract the hydrolytic activity of these enzymes, combinations of a β-lactam with a β-lactamase inhibitor (BLI) have been clinically successful. However, some β-lactam-BLI combinations have lost their effectiveness against prevalent Gram-negative pathogens that produce ESBLs, carbapenemases or multiple β-lactamases in the same organism. In this Review, descriptions are provided for medically relevant β-lactamase families and various BLI combinations that have been developed or are under development. Recently approved inhibitor combinations include the inhibitors avibactam and vaborbactam of the diazabicyclooctanone and boronic acid inhibitor classes, respectively, as new scaffolds for future inhibitor design.

The latest advances in β-lactam/β-lactamase inhibitor combinations for the treatment of Gram-negative bacterial infections

Introduction: Antimicrobial resistance in Gram-negative pathogens is a significant threat to global health. β-Lactams (BL) are one of the safest and most-prescribed classes of antibiotics on the market today. The acquisition of β-lactamases, especially those which hydrolyze carbapenems, is eroding the efficacy of BLs for the treatment of serious infections. During the past decade, significant advances were made in the development of novel BL-β-lactamase inhibitor (BLI) combinations to target β-lactamase-mediated resistant Gram-negatives.Areas covered: The latest progress in 20 different approved, developing, and preclinical BL-BLI combinations to target serine β-lactamases produced by Gram-negatives are reviewed based on primary literature, conference abstracts (when available), and US clinical trial searches within the last 5 years. The majority of the compounds that are discussed are being evaluated as part of a BL-BLI combination.Expert opinion: The current trajectory in BLI development is promising; however, a significant challenge resides in the selection of an appropriate BL partner as well as the development of resistance linked to the BL partner. In addition, dosing regimens for these BL-BLI combinations need to be critically evaluated. A revolution in bacterial diagnostics is essential to aid clinicians in the appropriate selection of novel BL-BLI combinations for the treatment of serious infections.

Antibiotic resistance pattern of Acinetobacter baumannii from burns patients: increase in prevalence of bla OXA-24-like and bla OXA-58-like genes

BACKGROUND AND OBJECTIVES

Notwithstanding the increased prevalence of Acinetobacter baumannii drug-resistant isolates, treatment options are progressively limiting. This study aims to provide a recent report on antibiotic susceptibility in burn wound isolates of A. baumannii, and the importance of OXA beta-lactamases in carbapenem resistance.

MATERIALS AND METHODS

The susceptibility levels to different antimicrobial categories were determined among 84 A. baumannii isolates from burn wound infection between 2016 and 2018. Multiplex PCR was used to detect OXA beta-lactamases genes, including bla _OXA-51, bla _OXA-23, bla _OXA-24 and bla _OXA-58. ISAba-1 association with bla _OXA-51, bla _OXA-23 and bla _OXA-58 was detected by PCR mapping.

RESULTS

All the isolates were determined as multidrug-resistant (MDR) and 69% as extensively drug-resistant (XDR). Different carbapenems MIC ranges (MIC₅₀ and MIC₉₀) were observed among the isolates harboring bla _OXA-like genes and isolates with the OXA-24-like enzyme showed higher carbapenems MIC ranges. The prevalence of bla _OXA-51-like, bla _OXA-23-like, bla _OXA-24-like and bla _OXA-58-like were 100%, 53.57%, 41.66% and 30.95%, respectively. ISAba-1 insertion sequence was found to be upstream to bla _OXA-23-like and bla _OXA-58-like genes in 23 out of 45 (71.1%) bla _OXA-23-like-positive and 4 out of 23 (15.3) bla _OXA-58-like-positive isolates, respectively.

CONCLUSION

Resistance to carbapenems as the last resort for treatment of A. baumannii infections is growing. This study, for the first time in Iran, has observed the increased frequency of bla _OXA-24-like and bla _OXA-58-like genes and found an association between ISAba-1 and bla _OXA-58-like gene, which signifies the possible risk of increased diversity in OXA beta-lactamases and growth in carbapenem resistance.

The Global Ascendency of OXA-48-Type Carbapenemases

Surveillance studies have shown that OXA-48-like carbapenemases are the most common carbapenemases in Enterobacterales in certain regions of the world and are being introduced on a regular basis into regions of nonendemicity, where they are responsible for nosocomial outbreaks. OXA-48, OXA-181, OXA-232, OXA-204, OXA-162, and OXA-244, in that order, are the most common enzymes identified among the OXA-48-like carbapenemase group. OXA-48 is associated with different Tn1999 variants on IncL plasmids and is endemic in North Africa and the Middle East. OXA-162 and OXA-244 are derivatives of OXA-48 and are present in Europe. OXA-181 and OXA-232 are associated with ISEcp1, Tn2013 on ColE2, and IncX3 types of plasmids and are endemic in the Indian subcontinent (e.g., India, Bangladesh, Pakistan, and Sri Lanka) and certain sub-Saharan African countries. Overall, clonal dissemination plays a minor role in the spread of OXA-48-like carbapenemases, but certain high-risk clones (e.g., Klebsiella pneumoniae sequence type 147 [ST147], ST307, ST15, and ST14 and Escherichia coli ST38 and ST410) have been associated with the global dispersion of OXA-48, OXA-181, OXA-232, and OXA-204. Chromosomal integration of bla _OXA-48 within Tn6237 occurred among E. coli ST38 isolates, especially in the United Kingdom. The detection of Enterobacterales with OXA-48-like enzymes using phenotypic methods has improved recently but remains challenging for clinical laboratories in regions of nonendemicity. Identification of the specific type of OXA-48-like enzyme requires sequencing of the corresponding genes. Bacteria (especially K. pneumoniae and E. coli) with bla _OXA-48, bla _OXA-181, and bla _OXA-232 are emerging in different parts of the world and are most likely underreported due to problems with the laboratory detection of these enzymes. The medical community should be aware of the looming threat that is posed by bacteria with OXA-48-like carbapenemases.