In vitro activity of cefepime/zidebactam (WCK 5222) against Gram-negative bacteria

In vitro activity and resistance mechanisms of novel antimicrobial agents against metallo-β-lactamase producers

The carbapenemase-producing Gram-negative organisms represent an urgent clinical and public health concern, as they have been associated with increased mortality and high dissemination in healthcare settings. Although overall incidence rates of infections sustained by metallo-β-lactamase (MβL)-producers have remained lower than those sustained by other carbapenemase-producers, albeit with substantial geographic differences, a significant increase in the prevalence of MβL-producers has been observed over the last decade. The recent development of new antimicrobials expanded the armamentarium to counter the challenge of metallo-β-lactamase (MβL)-producers. Cefiderocol and aztreonam/avibactam are already clinically available and recommended by international guidelines. In addition, two new classes of β-lactam/ β-lactamase combinations are under clinical evaluation: (i) combination of β-lactam with novel boronic-derived inhibitors (e.g. taniborbactam and xeruborbactam), (ii) combination of β-lactam with last generation diazabicyclooctane β-lactamase inhibitors (e.g. zidebactam and nacubactam), active on most of serine-β-lactamases but also showing strong intrinsic activity on PBP-2. This review aims to provide up-to-date data on the characteristics, activity and emerging resistance mechanisms of the armamentarium of clinically available or soon-to-be introduced drugs for the treatment of MβL-producing Gram-negative organisms.

Antibacterials with Novel Chemical Scaffolds in Clinical Development

The rise of antimicrobial resistance represents a significant global health threat, driven by the diminishing efficacy of existing antibiotics, a lack of novel antibacterials entering the market, and an over- or misuse of existing antibiotics, which accelerates the evolution of resistant bacterial strains. This review focuses on innovative therapies by highlighting 19 novel antibacterials in clinical development as of June 2024. These selected compounds are characterized by new chemical scaffolds, novel molecular targets, and/or unique mechanisms of action, which render their potential to break antimicrobial resistance particularly high. A detailed analysis of the scientific foundations behind each of these compounds is provided, including their pharmacodynamic profiles, current development state, and potential for overcoming existing limitations in antibiotic therapy. By presenting this subset of chemically novel antibacterials, the review highlights the ability to innovate in antibiotic drug development to counteract bacterial resistance and improve treatment outcomes.

β-Lactam/β-Lactamase Inhibitor Combination Antibiotics Under Development

Antimicrobial resistance remains a public health problem of global concern with a great health and financial burden. Its recognition as a threat by political leadership has boosted the research and development of new antibiotics and particularly novel combinations of β-lactams/β-lactamase inhibitors against multidrug-resistant (MDR) Gram-negative pathogens, which remain the major concern in clinical practice. The incorporation of ceftolozane/tazobactam, ceftazidime/avibactam, meropenem/vaborbactam, and imipenem/cilastatin/relebactam has provided new therapeutic options in the treatment of patients with infections due to MDR pathogens. Cefiderocol along with cefepime/enmetazobactam, avibactam/aztreonam, and sulbactam/durlobactam have been recently added to these agents as therapeutic choices, particularly for metallo-β-lactamase producing Gram-negative bacteria. Currently, many combinations are being studied for their in vitro activity against both serine- and metallo-β-lactamases. However, only a few have advanced through phase 1, 2, and 3 clinical trials. Among them, in this article, we focus on the most promising combinations of cefepime/zidebactam, cefepime/taniborbactam, and imipenem/cilastatin/funobactam, which are currently under investigation in phase 3 trials.

Novel Variant of New Delhi Metallo-Beta-Lactamase (blaNDM-60) Discovered in a Clinical Strain of Escherichia coli from the United Arab Emirates: An Emerging Challenge in Antimicrobial Resistance

Background/Objectives: Carbapenem resistance poses a significant health threat. This study reports the first detection and characterization of a novel variant of New Delhi metallo-β-lactamase (blaNDM-60) in Escherichia coli from the United Arab Emirates (UAE), including its genetic context and relationship to global strains. Methods: NDM-60-producing E. coli was isolated from a rectal swab during routine screening. Characterization involved whole-genome sequencing, antimicrobial susceptibility testing, and comparative genomic analysis with 66 known NDM variants. Core genome analysis was performed against 42 global E. coli strains, including the single other reported NDM-60-positive isolate. Results: The strain demonstrated extensive drug resistance, including resistance to novel β-lactam/β-lactamase inhibitor combinations, notably taniborbactam. NDM-60 differs from the closely related NDM-5 by a single amino acid substitution (Asp202Asn) and two amino acid substitutions (Val88Leu and Met154Leu) compared to NDM-1. NDM-60 is located on a nonconjugative IncX3 plasmid. The strain belongs to sequence type 940 (ST940). Phylogenetic analysis revealed high diversity among the global ST940 strains, which carry a plethora of resistance genes and originated from humans, animals, and the environment from diverse geographic locations. Conclusions: NDM-60 emergence in the UAE represents a significant evolution in carbapenemase diversity. Its presence on a nonconjugative plasmid may limit spread; however, its extensive resistance profile is concerning. Further studies are needed to determine the prevalence, dissemination, and clinical impact of NDM-60. NDM evolution underscores the ongoing challenge in managing antimicrobial resistance and the critical importance of vigilant molecular surveillance. It also highlights the pressing demand to discover new antibiotics to fight resistant bacteria.

New antibiotics in clinical pipeline for treating infections caused by metallo-β-lactamases producing Gram-negative bacteria

PURPOSE OF REVIEW

To discuss novel antibiotics under clinical development, focusing on agents showing in-vitro activity against metallo-β-lactamases (MBL)-producing carbapenem-resistant Gram-negative bacteria (CR-GNB).

RECENT FINDINGS

Currently, only a few approved agents show activity, alone or in synergistic combinations, against MBL-producing CR-GNB. If approved by regulatory agencies in case of favorable results from ongoing (and, for some agents, already completed) phase-3 studies, some novel β-lactam/β-lactamase inhibitor (BL/BLI) combinations could become available in the next few years as additional important options for treating MBL-producing CR-GNB infections. Additional interesting agents that belong both to BL/BLI combinations and to antibiotic classes other than BL and BL/BLI combinations have also shown activity against MBL-producing CR-GNB, with most of them being in early phases of clinical development.

SUMMARY

Improving the use of these novel agents through virtuous antimicrobial stewardship frameworks able to guarantee both the efficacious treatment of infections requiring their use and the avoidance of their use whenever not necessary remains a challenge of utmost importance that should not be overlooked.

Navigating the Current Treatment Landscape of Metallo-β-Lactamase-Producing Gram-Negative Infections: What are the Limitations?

The spread of carbapenemase-producing gram-negative pathogens, especially those producing metallo-β-lactamases (MBLs), has become a major health concern. MBLs are molecularly the most diverse carbapenemases, produced by a wide spectrum of gram-negative organisms, including the Enterobacterales, Pseudomonas spp., Acinetobacter baumannii, and Stenotrophomonas maltophilia, and can hydrolyze most β-lactams using metal ion cofactors in their active sites. Over the years, the prevalence of MBL-carrying isolates has increased globally, particularly in Asia. MBL infections are associated with adverse clinical outcomes including longer length of hospital stay, ICU admission, and increased mortality across the globe. The optimal treatment for MBL infections not only depends on the pathogen but also on the underlying resistance mechanisms. Currently, there are only few drugs or drug combinations that can efficiently offset MBL-mediated resistance, which makes the treatment of MBL infections challenging. The rising concern of MBLs along with the limited treatment options has led to the need and development of drugs that are specifically targeted towards MBLs. This review discusses the prevalence of MBLs, their clinical impact, and the current treatment options for MBL infections and their limitations. Furthermore, this review will discuss agents currently in the pipeline for treatment of MBL infections.

Novel agents in development for the treatment of resistant Gram-negative infections

INTRODUCTION

Several novel agents are in advanced stages of clinical development, potentially expanding our treatment options against third- and fourth-generation cephalosporin-resistant and carbapenem-resistant Gram-negative bacteria (GNB), including those pathogens for which the current number of effective treatments is limited.

AREAS COVERED

This review focuses on agents that have completed or ongoing phase-3 studies. A PubMed search was conducted up to 31 May 2024.

EXPERT OPINION

Novel agents in late-stage clinical development belong to the β-lactam or β-lactam/β-lactamase inhibitor combinations class and display variable antimicrobial activity depending on the specific β-lactamases expressed by GNB, particularly carbapenemases. While many of these novel agents demonstrate in vitro activity against carbapenem-resistant GNB, their efficacy has mainly been evaluated in phase-3 randomized controlled trials (RCT) for infections caused by carbapenem-susceptible GNB. Although evidence from real-world observational studies is generally less robust than that from RCT, it could be crucial for updating clinical guidelines on treating carbapenem-resistant GNB with these new agents in the absence of dedicated RCT.

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.

Rapid Emergence of Resistance to Broad-Spectrum Direct Antimicrobial Activity of Avibactam

Avibactam (AVI) is a diazabicyclooctane (DBO) β-lactamase inhibitor used clinically in combination with ceftazidime. At concentrations higher than those typically achieved in vivo, it also has broad-spectrum direct antibacterial activity against Enterobacterales strains, including metallo-β-lactamase-producing isolates, mediated by inhibition of penicillin-binding protein 2 (PBP2). This activity is mechanistically similar to that of more potent novel DBOs (zidebactam, nacubactam) in late clinical development. We found that resistance to AVI emerged readily, with a mutation frequency of 2×10-6 to 8×10-5. Whole genome sequencing of resistant isolates revealed a heterogeneous mutational target that permitted bacterial survival and replication despite PBP2 inhibition, in line with prior studies of PBP2-targeting drugs. While such mutations are believed to act by upregulating the bacterial stringent response, we found a similarly high mutation frequency in bacteria deficient in components of the stringent response, although we observed a different set of mutations in these strains. Although avibactam-resistant strains had increased lag time, suggesting a fitness cost that might render them less problematic in clinical infections, there was no statistically significant difference in growth rates between susceptible and resistant strains. The finding of rapid emergence of resistance to avibactam as the result of a large mutational target has important implications for novel DBOs with potent direct antibacterial activity, which are being developed with the goal of expanding cell wall-active treatment options for multidrug-resistant gram-negative infections but may be vulnerable to treatment-emergent resistance.

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.

Unveiling the Secrets of Acinetobacter baumannii: Resistance, Current Treatments, and Future Innovations

Acinetobacter baumannii represents a significant concern in nosocomial settings, particularly in critically ill patients who are forced to remain in hospital for extended periods. The challenge of managing and preventing this organism is further compounded by its increasing ability to develop resistance due to its extraordinary genomic plasticity, particularly in response to adverse environmental conditions. Its recognition as a significant public health risk has provided a significant impetus for the identification of new therapeutic approaches and infection control strategies. Indeed, currently used antimicrobial agents are gradually losing their efficacy, neutralized by newer and newer mechanisms of bacterial resistance, especially to carbapenem antibiotics. A deep understanding of the underlying molecular mechanisms is urgently needed to shed light on the properties that allow A. baumannii enormous resilience against standard therapies. Among the most promising alternatives under investigation are the combination sulbactam/durlobactam, cefepime/zidebactam, imipenem/funobactam, xeruborbactam, and the newest molecules such as novel polymyxins or zosurabalpin. Furthermore, the potential of phage therapy, as well as deep learning and artificial intelligence, offer a complementary approach that could be particularly useful in cases where traditional strategies fail. The fight against A. baumannii is not confined to the microcosm of microbiological research or hospital wards; instead, it is a broader public health dilemma that demands a coordinated, global response.

Spread of carbapenemase-producing Morganella spp from 2013 to 2021: a comparative genomic study

BACKGROUND

Morganella spp are opportunistic pathogens involved in various infections. Intrinsic resistance to multiple antibiotics (including colistin) combined with the emergence of carbapenemase producers reduces the number of active antimicrobials. The aim of this study was to characterise genetic features related to the spread of carbapenem-resistant Morganella spp.

METHODS

This comparative genomic study included extensively drug-resistant Morganella spp isolates collected between Jan 1, 2013, and March 1, 2021, by the French National Reference Center (NRC; n=68) and European antimicrobial resistance reference centres in seven European countries (n=104), as well as one isolate from Canada, two reference strains from the Pasteur Institute collection (Paris, France), and two colistin-susceptible isolates from Bicêtre Hospital (Kremlin-Bicêtre, France). The isolates were characterised by whole-genome sequencing, antimicrobial susceptibility testing, and biochemical tests. Complete genomes from GenBank (n=103) were also included for genomic analysis, including phylogeny and determination of core genomes and resistomes. Genetic distance between different species or subspecies was performed using average nucleotide identity (ANI). Intrinsic resistance mechanisms to polymyxins were investigated by combining genetic analysis with mass spectrometry on lipid A.

FINDINGS

Distance analysis by ANI of 275 isolates identified three groups: Morganella psychrotolerans, Morganella morganii subspecies sibonii, and M morganii subspecies morganii, and a core genome maximum likelihood phylogenetic tree showed that the M morganii isolates can be separated into four subpopulations. On the basis of these findings and of phenotypic divergences between isolates, we propose a modified taxonomy for the Morganella genus including four species, Morganella psychrotolerans, Morganella sibonii, Morganella morganii, and a new species represented by a unique environmental isolate. We propose that M morganii include two subspecies: M morganii subspecies morganii (the most prevalent) and M morganii subspecies intermedius. This modified taxonomy was supported by a difference in intrinsic resistance to tetracycline and conservation of metabolic pathways such as trehalose assimilation, both only present in M sibonii. Carbapenemase producers were mostly identified among five high-risk clones of M morganii subspecies morganii. The most prevalent carbapenemase corresponded to NDM-1, followed by KPC-2, and OXA-48. A cefepime-zidebactam combination was the most potent antimicrobial against the 172 extensively drug-resistant Morganella spp isolates in our collection from different European countries, which includes metallo-β-lactamase producers. Lipid A analysis showed that the intrinsic resistance to colistin was associated with the presence of L-ARA4N on lipid A.

INTERPRETATION

This global characterisation of, to our knowledge, the widest collection of extensively drug-resistant Morganella spp highlights the need to clarify the taxonomy and decipher intrinsic resistance mechanisms, and paves the way for further genomic comparisons.

FUNDING

None.

Cephalosporin resistance, tolerance, and approaches to improve their activities

Cephalosporins comprise a β-lactam antibiotic class whose first members were discovered in 1945 from the fungus Cephalosporium acremonium. Their clinical use for Gram-negative bacterial infections is widespread due to their ability to traverse outer membranes through porins to gain access to the periplasm and disrupt peptidoglycan synthesis. More recent members of the cephalosporin class are administered as last resort treatments for complicated urinary tract infections, MRSA, and other multi-drug resistant pathogens, such as Neisseria gonorrhoeae. Unfortunately, there has been a global increase in cephalosporin-resistant strains, heteroresistance to this drug class has been a topic of increasing concern, and tolerance and persistence are recognized as potential causes of cephalosporin treatment failure. In this review, we summarize the cephalosporin antibiotic class from discovery to their mechanisms of action, and discuss the causes of cephalosporin treatment failure, which include resistance, tolerance, and phenomena when those qualities are exhibited by only small subpopulations of bacterial cultures (heteroresistance and persistence). Further, we discuss how recent efforts with cephalosporin conjugates and combination treatments aim to reinvigorate this antibiotic class.

Multidrug-resistant Gram-negative clinical isolates with reduced susceptibility/resistance to cefiderocol: which are the best present and future therapeutic alternatives?

PURPOSE

To evaluate the different present and future therapeutic β-lactam/β-lactamase inhibitor (BL/BLI) alternatives, namely aztreonam-avibactam, imipenem-relebactam, meropenem-vaborbactam, cefepime-zidebactam, cefepime-taniborbactam, meropenem-nacubactam, and sulbactam-durlobactam against clinical isolates showing reduced susceptibility or resistance to cefiderocol in Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa.

METHODS

MIC values of aztreonam, aztreonam-avibactam, cefepime, cefepime-taniborbactam, cefepime-zidebactam, imipenem, imipenem-relebactam, meropenem, meropenem-vaborbactam, meropenem-nacubactam, sulbactam-durlobactam, and cefiderocol combined with a BLI were determined for 67, 9, and 11 clinical Enterobacterales, P. aeruginosa or A. baumannii isolates, respectively, showing MIC values of cefiderocol being ≥1 mg/L. If unavailable, the respective β-lactam breakpoints according to EUCAST were used for BL/BLI combinations.

RESULTS

For Enterobacterales, the susceptibility rates for aztreonam, cefepime, imipenem, and meropenem were 7.5%, 0%, 10.4%, and 10.4%, respectively, while they were much higher for cefepime-zidebactam (91%), cefiderocol-zidebactam (91%), meropenem-nacubactam (71.6%), cefiderocol-nacubactam (74.6%), and cefiderocol-taniborbactam (76.1%), as expected. For P. aeruginosa isolates, the higher susceptibility rates were observed for imipenem-relebactam, cefiderocol-zidebactam, and meropenem-vaborbactam (56% for all combinations). For A. baumannii isolates, lower susceptibility rates were observed with commercially or under development BL/BLI combos; however, a high susceptibility rate (70%) was found for sulbactam-durlobactam and when cefiderocol was associated to some BLIs.

CONCLUSIONS

Zidebactam- and nacubactam-containing combinations showed a significant in vitro activity against multidrug-resistant Enterobacterales clinical isolates with reduced susceptibility to cefiderocol. On the other hand, imipenem-relebactam and meropenem-vaborbactam showed the highest susceptibility rates against P. aeruginosa isolates. Finally, sulbactam-durlobactam and cefiderocol combined with a BLI were the only effective options against A. baumannii tested isolates.

Novel metallo-β-lactamases inhibitors restore the susceptibility of carbapenems to New Delhi metallo-lactamase-1 (NDM-1)-harbouring bacteria

BACKGROUND AND PURPOSE

The production of metallo-β-lactamases is a major mechanisms adopted by bacterial pathogens to resist carbapenems. Repurposing approved drugs to restore the efficacy of carbapenems represents an efficient and cost-effective approach to fight infections caused by carbapenem resistant pathogens.

EXPERIMENTAL APPROACH

The nitrocefin hydrolysis assay was employed to screen potential New Delhi metallo-lactamase-1 (NDM-1) inhibitors from a commercially available U.S. Food and Drug Administration (FDA) approved drug library. The mechanism of inhibition was clarified by metal restoration, inductively coupled plasma mass spectrometry (ICP-MS) and molecular dynamics simulation. The in vitro synergistic antibacterial effect of the identified inhibitors with meropenem was determined by the checkerboard minimum inhibitory concentration (MIC) assay, time-dependent killing assay and combined disc test. Three mouse infection models were used to further evaluate the in vivo therapeutic efficacy of combined therapy.

KEY RESULTS

Twelve FDA-approved compounds were initially screened to inhibit the ability of NDM-1 to hydrolyse nitrocefin. Among these compounds, dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid were demonstrated to inhibit all tested metallo-β-lactamases and showed an in vitro synergistic bactericidal effect with meropenem against metallo-β-lactamases-producing bacteria. Dexrazoxane, embelin and candesartan cilexetil are metal ion chelating agents, while the inhibition of NDM-1 by nordihydroguaiaretic acid involves its direct binding to the active region of NDM-1. Furthermore, these four drugs dramatically rescued the treatment efficacy of meropenem in three infection models.

CONCLUSIONS AND IMPLICATIONS

Our observations indicated that dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid are promising carbapenem adjuvants against metallo-β-lactamases-positive carbapenem resistant bacterial pathogens.

Antibiotic therapy for nonfermenting Gram-negative bacilli infections: future perspectives

PURPOSE OF REVIEW

Serious infections caused by nonfermenting Gram-negative bacteria (NF-GNB) pose a significant challenge for clinicians due to the limited treatment options available, which are frequently associated with issues of toxicity and unfavourable pharmacokinetic profiles. The aim of this review is to provide a brief overview of the existing data concerning the ongoing development of antiinfective agents targeting NF-GNB.

RECENT FINDINGS

Several agents exhibiting efficacy against NF-GNB are under clinical investigation. Durlobactam-sulbactam and cefepime-taniborbactam emerge as promising therapeutic avenues against carbapenem-resistant Acinetobacter baumanii . Cefepime-zidebactam may serve as a suitable treatment option for urinary tract infections caused by a wide range of NF-GNB. Cefepime-enmetazobactam demonstrates potent in vitro activity against various NF-GNB strains; however, its role as an anti- Pseudomonal agent is inadequately substantiated by available data. Xeruborbactam is a wide β-lactamase inhibitor that can be associated with a range of agents, enhancing in-vitro activity of these against many NF-GNB, including those resistant to newer, broader spectrum options. Lastly, murepavadin appears to be a potential pathogen-specific solution for severe Pseudomonas infections; however, additional investigation is necessary to establish the safety profile of this compound.

SUMMARY

Each of the novel molecules reviewed possesses an interesting range of in-vitro activity against NF-GNB. In addition, some of them have already been proved effective in vivo, underscoring their potential as future treatment options.

Case Commentary: Successful Use of Cefepime/Zidebactam (WCK 5222) as a Salvage Therapy for the Treatment of Disseminated Extensively Drug-Resistant New Delhi Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Infection in an Adult Patient with Acute T-Cell Leukemia

Multidrug-resistant/extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa (PA) are critical antimicrobial resistance threats. Despite their increasing prevalence, treatment options for metallo-β-lactamase (MBL)-producing PA are limited, especially for New Delhi metallo-β-lactamase (NDM) producers. Pending further clinical studies, this case provides support for limited-scope use of cefepime-zidebactam for treating disseminated infections secondary to NDM-producing XDR PA. Susceptibilities should be tested and/or alternative regimens considered when treating isolates with alternative MBLs or increased efflux pump expression because some in vitro data suggest associated loss of cefepime-zidebactam susceptibility.

Successful Use of Cefepime-Zidebactam (WCK 5222) as a Salvage Therapy for the Treatment of Disseminated Extensively Drug-Resistant New Delhi Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Infection in an Adult Patient with Acute T-Cell Leukemia

With limited and often toxic treatment options, carbapenem-resistant Gram-negative infections are associated with significant mortality. Cefepime-zidebactam is a promising antibiotic option undergoing a phase 3 trial that has activity against diverse antibiotic-resistant mechanisms in Gram-negative pathogens due to its β-lactam enhancer mechanism, mediating multiple PBP binding. We report a case of disseminated infection caused by a New Delhi metallo-β-lactamase-producing, extensively drug-resistant Pseudomonas aeruginosa isolate in a patient with acute T-cell leukemia, successfully managed with cefepime-zidebactam as a salvage therapy.

β-Lactam Resistance in ESKAPE Pathogens Mediated Through Modifications in Penicillin-Binding Proteins: An Overview

Bacteria acquire β-lactam resistance through a multitude of mechanisms among which production of β-lactamases (enzymes that hydrolyze β-lactams) is the most common, especially in Gram-negatives. Structural changes in the high-molecular-weight, essential penicillin-binding proteins (PBPs) are widespread in Gram-positives and increasingly reported in Gram-negatives. PBP-mediated resistance is largely achieved by accumulation of mutation(s) resulting in reduced binding affinities of β-lactams. Herein, we discuss PBP-mediated resistance among ESKAPE pathogens that cause diverse hospital- and community-acquired infections globally.

Off-label use versus formal recommendations of conventional and novel antibiotics for the treatment of infections caused by multidrug-resistant bacteria

The infections caused by multidrug- and extensively drug-resistant (MDR, XDR) bacteria, including Gram-positive cocci (GPC, including methicillin-resistant Staphylococcus aureus, MDR-Streptococcus pneumoniae and vancomycin-resistant enterococci) and Gram-negative bacilli (GNB, including carbapenem-resistant [CR] Enterobacterales, CR-Pseudomonas aeruginosa and XDR/CR-Acinetobacter baumannii complex) can be quite challenging for physicians with respect to treatment decisions. Apart from complicated urinary tract and intra-abdominal infections (cUTIs, cIAIs), bloodstream infections and pneumonia, these difficult-to-treat bacteria also cause infections at miscellaneous sites (bones, joints, native/prosthetic valves and skin structures, etc.). Antibiotics like dalbavancin, oritavancin, telavancin and daptomycin are currently approved for the treatment of acute bacterial skin and skin structural infections (ABSSSIs) caused by GPC. Additionally, ceftaroline, linezolid and tigecycline have been formally approved for the treatment of community-acquired pneumonia and ABSSSI. Cefiderocol and meropenem-vaborbactam are currently approved for the treatment of cUTIs caused by XDR-GNB. The spectra of ceftazidime-avibactam and imipenem/cilastatin-relebactam are broader than that of ceftolozane-tazobactam, but these three antibiotics are currently approved for the treatment of hospital-acquired pneumonia, cIAIs and cUTIs caused by MDR-GNB. Clinical investigations of other novel antibiotics (including cefepime-zidebactam, aztreonam-avibactam and sulbactam-durlobactam) for the treatment of various infections are ongoing. Nevertheless, evidence for adequate antibiotic regimens against osteomyelitis, arthritis and infective endocarditis due to several GPC and MDR-GNB is still mostly lacking. A comprehensive review of PubMed publications was undertaken and the formal indications and off-label use of important conventional and novel antibiotics against MDR/XDR-GPC and GNB isolates cultured from miscellaneous sites are presented in this paper.

In vitro activity of aztreonam in combination with newly developed β-lactamase inhibitors against MDR Enterobacterales and Pseudomonas aeruginosa producing metallo-β-lactamases

OBJECTIVES

To evaluate the in vitro activity of aztreonam in combination with novel β-lactamase inhibitors, namely avibactam, nacubactam, taniborbactam and zidebactam, against MDR MBL-producing Enterobacterales and Pseudomonas aeruginosa clinical isolates.

METHODS

MIC values of aztreonam, aztreonam/β-lactam inhibitor but also cefiderocol as comparator were determined for 64 and 39 clinical Enterobacterales or P. aeruginosa isolates, respectively, producing representative MBLs, i.e. derivatives of NDM (n = 64), VIM (n = 32), IMP (n = 8) and SPM (n = 2). MICs were also determined for Escherichia coli TOP10 and P. aeruginosa PAO1 harbouring recombinant plasmids producing the different β-lactamases under isogenic backgrounds (n = 22 and n = 11, respectively). Fifty percent inhibitory concentrations were additionally determined for the abovementioned β-lactamase inhibitors using β-lactamase crude extracts.

RESULTS

The susceptibility rate for aztreonam was 17.1% among MBL-producing Enterobacterales, while it was very high with aztreonam/zidebactam (98.4%), and to a lower extent with aztreonam/nacubactam (84.4%) and aztreonam/taniborbactam (75%), compared with aztreonam/avibactam (70.3%) and cefiderocol (39.1%). Among MBL-producing P. aeruginosa isolates, the susceptibility rates were 53.8% with aztreonam, 66.7% with aztreonam/nacubactam and aztreonam/taniborbactam combinations, and 69.2% with aztreonam/avibactam, aztreonam/zidebactam and cefiderocol.

CONCLUSIONS

Altogether, these results showed that combinations including aztreonam and novel β-lactamase inhibitors, such as zidebactam, nacubactam or taniborbactam, have a very significant in vitro activity against MDR MBL-producing Enterobacterales clinical isolates, the aztreonam/zidebactam combination being the best option. On the other hand, aztreonam/zidebactam is equivalent to aztreonam/avibactam and cefiderocol among MBL-producing P. aeruginosa isolates.

Antibiotics in development for multiresistant gram-negative bacilli

The rapid increase in antibiotic(ATB) resistance among Gram-negative bacilli(BGN), especially in strains of Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii, with high resistance patterns (XDR), poses a huge threat to health systems worldwide. In the last decade, different ATBs have been developed against XDR, some of which combine a lactam β along with a β-lactamase inhibitor, while others use non-β-lactam inhibitors. Most of them have adequate "in vitro" activity on several β-lactamases of class A, C and D of Ambler. However, combinations such as Ceftazidime/avibactam, Ceftolozane/Tazobactam and Meropenem/vaborbactam have no activity against metallo-β-lactamases(MβL). New combinations such as Aztreonan/AVI, Cefepime/Zidebactam, or new cephalosporins such as Cefiderocol, have efficacy against MβL enzymes. Although some of these combinations are already approved and in the commercialization phase, many of them have yet to define their place within the treatment of microorganisms with high resistance through clinical studies.

Drug development concerning metallo-β-lactamases in gram-negative bacteria

β-Lactams have been a clinical focus since their emergence and indeed act as a powerful tool to combat severe bacterial infections, but their effectiveness is threatened by drug resistance in bacteria, primarily by the production of serine- and metallo-β-lactamases. Although once of less clinical relevance, metallo-β-lactamases are now increasingly threatening. The rapid dissemination of resistance mediated by metallo-β-lactamases poses an increasing challenge to public health worldwide and comprises most existing antibacterial chemotherapies. Regrettably, there have been no clinically available inhibitors of metallo-β-lactamases until now. To cope with this unique challenge, researchers are exploring multidimensional strategies to combat metallo-β-lactamases. Several studies have been conducted to develop new drug candidates or calibrate already available drugs against metallo-β-lactamases. To provide an overview of this field and inspire more researchers to explore it further, we outline some promising candidates targeting metallo-β-lactamase producers, with a focus on Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. Promising candidates in this review are composed of new antibacterial drugs, non-antibacterial drugs, antimicrobial peptides, natural products, and zinc chelators, as well as their combinations with existing antibiotics. This review may provide ideas and insight for others to explore candidate metallo-β-lactamases as well as promote the improvement of existing data to obtain further convincing evidence.

Intrinsic Antibacterial Activity of Xeruborbactam In Vitro : Assessing Spectrum and Mode of Action

Xeruborbactam (formerly QPX7728) is a cyclic boronate inhibitor of numerous serine and metallo-beta-lactamases. At concentrations generally higher than those required for beta-lactamase inhibition, xeruborbactam has direct antibacterial activity against some Gram-negative bacteria, with MIC₅₀/MIC₉₀ values of 16/32 μg/mL and 16/64 μg/mL against carbapenem-resistant Enterobacterales and carbapenem-resistant Acinetobacter baumannii, respectively (the MIC₅₀/MIC₉₀ values against Pseudomonas aeruginosa are >64 μg/mL). In Klebsiella pneumoniae, inactivation of OmpK36 alone or in combination with OmpK35 resulted in 2- to 4-fold increases in the xeruborbactam MIC. In A. baumannii and P. aeruginosa, AdeIJK and MexAB-OprM, respectively, affected xeruborbactam’s antibacterial potency (the MICs were 4- to 16-fold higher in efflux-proficient strains). In Escherichia coli and K. pneumoniae, the 50% inhibitory concentrations (IC₅₀s) of xeruborbactam’s binding to penicillin-binding proteins (PBPs) PBP1a/PBP1b, PBP2, and PBP3 were in the 40 to 70 μM range; in A. baumannii, xeruborbactam bound to PBP1a, PBP2, and PBP3 with IC₅₀s of 1.4 μM, 23 μM, and 140 μM, respectively. Treating K. pneumoniae and P. aeruginosa with xeruborbactam at 1× and 2× MIC resulted in changes of cellular morphology similar to those observed with meropenem; the morphological changes observed after treatment of A. baumannii were consistent with inhibition of multiple PBPs but were unique to xeruborbactam compared to the results for control beta-lactams. No single-step xeruborbactam resistance mutants were obtained after selection at 4× MIC of xeruborbactam using wild-type strains of E. coli, K. pneumoniae, and A. baumannii; mutations selected at 2× MIC in K. pneumoniae did not affect antibiotic potentiation by xeruborbactam through beta-lactamase inhibition. Consistent with inhibition of PBPs, xeruborbactam enhanced the potencies of beta-lactam antibiotics even against strains that lacked beta-lactamase. In a large panel of KPC-producing clinical isolates, the MIC₉₀ values of meropenem tested with xeruborbactam (8 μg/mL) were at least 4-fold lower than those in combination with vaborbactam at 64 μg/mL, the concentration of vaborbactam that is associated with complete inhibition of KPC. The additional enhancement of the potency of beta-lactam antibiotics beyond beta-lactamase inhibition may contribute to the potentiation of beta-lactam antibiotics by xeruborbactam.

Treatment of MDR Gram-Negative Bacteria Infections: Ongoing and Prospective

Antimicrobial resistance is a serious public health concern across the world. Gram-negative resistance has propagated over the globe via various methods, the most challenging of which include extended-spectrum β-lactamases, carbapenemases, and AmpC enzymes. Gram-negative bacterial infections are difficult to treat in critically extremely sick persons. Resistance to different antibiotic treatments nearly always lowers the probability of proper empirical coverage, sometimes resulting in severe outcomes. Multidrug resistance can be combated with varying degrees of success using a combination of older drugs with high toxicity levels and novel therapeutics. The current therapies for multidrug-resistant Gram-negative bacteria are discussed in this review, which includes innovative medications, older pharmaceuticals, creative combinations of the two, and therapeutic targets.

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.

Antimicrobial activity of cefepime/zidebactam (WCK 5222), a β-lactam/β-lactam enhancer combination, against clinical isolates of Gram-negative bacteria collected worldwide (2018-19)

BACKGROUND

Zidebactam, a bicyclo-acyl hydrazide β-lactam 'enhancer' antibiotic, in combination with cefepime (WCK 5222) is under clinical development for the treatment of resistant Gram-negative infections.

OBJECTIVES

To evaluate the in vitro activity of cefepime/zidebactam and comparators against 24 220 Gram-negative bacteria.

METHODS

Organisms were consecutively collected in 2018-19 from 137 medical centres located in the USA (n = 9140), Western Europe (W-EU; n = 5929), Eastern Europe (E-EU; n = 3036), the Asia-Pacific region (APAC; n = 3791) and Latin America (LATAM; n = 2324). The isolates were susceptibility tested using the broth microdilution method as part of the SENTRY Program. Cefepime/zidebactam was tested at a 1:1 ratio.

RESULTS

Cefepime/zidebactam was highly active against Enterobacterales (MIC50/90 0.03/0.25 mg/L; 99.9% inhibited at ≤8 mg/L) and retained potent activity against carbapenem-resistant Enterobacterales (CRE) isolates (97.8% inhibited at ≤8 mg/L). CRE rates varied widely from 1.1% in the USA to 1.9% in W-EU, 3.6% in APAC and 14.6% in E-EU (3.9% overall). The most common carbapenemase genes observed overall were blaKPC (37.6% of CRE), blaOXA-48-like (30.0%) and blaNDM (23.8%). Resistance to ceftazidime/avibactam among CRE was elevated in APAC (64.8%), E-EU (25.5%) and LATAM (20.7%). Against Pseudomonas aeruginosa, cefepime/zidebactam inhibited 99.2% of isolates at ≤8 mg/L and susceptibility to ceftazidime/avibactam and ceftolozane/tazobactam was lowest in E-EU (83.9% and 82.0%, respectively). Cefepime/zidebactam exhibited good activity against Stenotrophomonas maltophilia (80.0% inhibited at ≤8 mg/L) and Burkholderia cepacia (89.4% inhibited at ≤8 mg/L).

CONCLUSIONS

Cefepime/zidebactam demonstrated potent in vitro activity against a large worldwide collection of contemporary clinical isolates of Gram-negative bacteria.

Microbiological, Clinical, and PK/PD Features of the New Anti-Gram-Negative Antibiotics: β-Lactam/β-Lactamase Inhibitors in Combination and Cefiderocol-An All-Inclusive Guide for Clinicians

Bacterial resistance mechanisms are continuously and rapidly evolving. This is particularly true for Gram-negative bacteria. Over the last decade, the strategy to develop new β-lactam/β-lactamase inhibitors (BLs/BLIs) combinations has paid off and results from phase 3 and real-world studies are becoming available for several compounds. Cefiderocol warrants a separate discussion for its peculiar mechanism of action. Considering the complexity of summarizing and integrating the emerging literature data of clinical outcomes, microbiological mechanisms, and pharmacokinetic/pharmacodynamic properties of the new BL/BLI and cefiderocol, we aimed to provide an overview of data on the following compounds: aztreonam/avibactam, cefepime/enmetazobactam, cefepime/taniborbactam, cefepime/zidebactam, cefiderocol, ceftaroline/avibactam, ceftolozane/tazobactam, ceftazidime/avibactam, imipenem/relebactam, meropenem/nacubactam and meropenem/vaborbactam. Each compound is described in a dedicated section by experts in infectious diseases, microbiology, and pharmacology, with tables providing at-a-glance information.

Global Threat of Carbapenem-Resistant Gram-Negative Bacteria

Infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria (GNB), including carbapenem-resistant (CR) Enterobacterales (CRE; harboring mainly bla_KPC, bla_NDM, and bla_OXA-48-like genes), CR- or MDR/XDR-Pseudomonas aeruginosa (production of VIM, IMP, or NDM carbapenemases combined with porin alteration), and Acinetobacter baumannii complex (producing mainly OXA-23, OXA-58-like carbapenemases), have gradually worsened and become a major challenge to public health because of limited antibiotic choice and high case-fatality rates. Diverse MDR/XDR-GNB isolates have been predominantly cultured from inpatients and hospital equipment/settings, but CRE has also been identified in community settings and long-term care facilities. Several CRE outbreaks cost hospitals and healthcare institutions huge economic burdens for disinfection and containment of their disseminations. Parenteral polymyxin B/E has been observed to have a poor pharmacokinetic profile for the treatment of CR- and XDR-GNB. It has been determined that tigecycline is suitable for the treatment of bloodstream infections owing to GNB, with a minimum inhibitory concentration of ≤ 0.5 mg/L. Ceftazidime-avibactam is a last-resort antibiotic against GNB of Ambler class A/C/D enzyme-producers and a majority of CR-P. aeruginosa isolates. Furthermore, ceftolozane-tazobactam is shown to exhibit excellent in vitro activity against CR- and XDR-P. aeruginosa isolates. Several pharmaceuticals have devoted to exploring novel antibiotics to combat these troublesome XDR-GNBs. Nevertheless, only few antibiotics are shown to be effective in vitro against CR/XDR-A. baumannii complex isolates. In this era of antibiotic pipelines, strict implementation of antibiotic stewardship is as important as in-time isolation cohorts in limiting the spread of CR/XDR-GNB and alleviating the worsening trends of resistance.

Molecular Characterization of WCK 5222 (Cefepime/Zidebactam)-Resistant Mutants Developed from a Carbapenem-Resistant Pseudomonas aeruginosa Clinical Isolate

WCK 5222 (cefepime/zidebactam) is a β-lactam/β-lactamase inhibitor combination that is effective against a broad range of highly drug-resistant bacterial pathogens, including those producing metallo-β-lactamase. In this study, we isolated a multidrug-resistant Pseudomonas aeruginosa clinical strain that is resistant to a variety of β-lactam antibiotics and the ceftazidime-avibactam combination. A metallo-β-lactamase gene blaDIM-2 was identified on a self-transmissible megaplasmid in the strain, which confers the resistance to β-lactam antibiotics, leaving WCK 5222 potentially one of the last treatment resorts. In vitro passaging assay combined with whole-genome sequencing revealed mutations in the pbpA gene (encoding the zidebactam target protein PBP2) in the evolved resistant mutants. Among the mutations, a V516M mutation increased the bacterial virulence in a murine acute pneumonia model. Reconstitution of the mutations in the reference strain PAO1 verified their roles in the resistance to zidebactam and revealed their influences on cell morphology in the absence and presence of zidebactam. Microscale thermophoresis (MST) assays demonstrated that the mutations reduced the affinity between PBP2 and zidebactam to various extents. Overall, our results revealed that mutations in the pbpA gene might be a major cause of evolved resistance to WCK 5222 in clinical settings. IMPORTANCE Antibiotic resistance imposes a severe threat on human health. WCK 5222 is a β-lactam/β-lactamase inhibitor combination that is composed of cefepime and zidebactam. It is one of the few antibiotics in clinical trials that are effective against multidrug-resistant Pseudomonas aeruginosa, including those producing metallo-β-lactamases. Understanding the mechanisms and development of bacterial resistance to WCK 5222 may provide clues for the development of strategies to suppress resistant evolvement. In this study, we performed an in vitro passaging assay by using a multidrug-resistant P. aeruginosa clinical isolate. Our results revealed that mutations in the zidebactam target protein PBP2 play a major role in the bacterial resistance to WCK 5222. We further demonstrated that the mutations reduced the affinities between PBP2 and zidebactam and resulted in functional resistance of PBP2 to zidebactam.

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.

Novel investigational treatments for ventilator-associated pneumonia and critically ill patients in the intensive care unit

INTRODUCTION

Ventilator-associated pneumonia (VAP) is common; its prevalence has been highlighted by the Covid-19 pandemic. Even young patients can suffer severe nosocomial infection and prolonged mechanical ventilation. Multidrug-resistant bacteria can spread alarmingly fast around the globe and new antimicrobials are struggling to keep pace; hence physicians must stay abreast of new developments in the treatment of nosocomial pneumonia and VAP.

AREAS COVERED

This narrative review examines novel antimicrobial investigational drugs and their implementation in the ICU setting for VAP. The paper highlights novel approaches such as monoclonal antibody treatments for P. aeruginosa and S. aureus, and phage antibiotic synthesis. The paper also examines mechanisms of resistance in gram-negative bacteria, virulence factors and inhaled antibiotics and questions what may be on the horizon in terms of emerging treatment strategies.

EXPERT OPINION

The post-antibiotic era is rapidly approaching and the need for personalised medicine, point-of-care microbial sensitivity testing and development of biomarkers for severe infections is clear. Results from emerging and new antibiotics are encouraging, but infection control measures and de-escalation protocols must be employed to prolong their usefulness in critical illness.

Molecular mechanisms underlying bacterial resistance to ceftazidime/avibactam

Ceftazidime/avibactam (CAZ/AVI), a combination of ceftazidime and a novel β-lactamase inhibitor (avibactam) that has been approved by the U.S. Food and Drug Administration, the European Union, and the National Regulatory Administration in China. CAZ/AVI is used mainly to treat complicated urinary tract infections and complicated intra-abdominal infections in adults, as well as to treat patients infected with Carbapenem-resistant Enterobacteriaceae (CRE) susceptible to CAZ/AVI. However, increased clinical application of CAZ/AVI has resulted in the development of resistant strains. Mechanisms of resistance in most of these strains have been attributed to bla_KPC mutations, which lead to amino acid substitutions in β-lactamase and changes in gene expression. Resistance to CAZ/AVI is also associated with reduced expression and loss of outer membrane proteins or overexpression of efflux pumps. In this review, the prevalence of CAZ/AVI-resistance bacteria, resistance mechanisms, and selection of detection methods of CAZ/AVI are demonstrated, aiming to provide scientific evidence for the clinical prevention and treatment of CAZ/AVI resistant strains, and provide guidance for the development of new drugs. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology.

OUP accepted manuscript

Objectives

Ertapenem has proven to be an effective antimicrobial; however, increasing enzyme-mediated resistance has been noted. Combination with zidebactam, a β-lactam enhancer, is restorative. Human-simulated regimens (HSRs) of ertapenem and zidebactam alone and in combination (WCK 6777; 2 g/2 g q24h) were assessed for efficacy against carbapenemase-producing Klebsiella pneumoniae (CP-KP) in the pneumonia model.

Methods

Infected ICR mice were rendered neutropenic and exposed to various doses of ertapenem and zidebactam alone and in combination to develop the HSRs that were subsequently confirmed in additional pharmacokinetic studies. Twenty-one CP-KP (KPC or OXA-48-like producers) with WCK 6777 MICs of 1–8 mg/L were utilized. Mice were treated for 24 h with saline or HSRs of ertapenem, zidebactam and WCK 6777. Efficacy was defined as change in mean lung bacterial density relative to 0 h.

Results

Confirmatory pharmacokinetic analysis showed agreement between predicted human exposures (%fT_>MIC) and those achieved in vivo for all three HSRs. The 0 h bacterial density across all isolates was 6.69 ± 0.31 log₁₀ cfu/lungs. At 24 h, densities increased by 2.57 ± 0.50, 2.2 ± 0.60 and 2.05 ± 0.71 log₁₀ cfu/lungs in the 24 h control, ertapenem HSR and zidebactam HSR groups, respectively. Overall, 18/21 of the isolates exposed to the WCK 6777 HSR displayed a killing profile that exceeded the translational benchmark for efficacy of a 1 log₁₀ cfu reduction. Among the remaining three isolates, two displayed ∼0.5 log₁₀ kill and stasis was observed in the third.

Conclusions

Human-simulated exposures of WCK 6777 demonstrated potent in vivo activity against CP-KP, including those with WCK 6777 MICs up to 8 mg/L.

Multicenter surveillance of in vitro activities of cefepime-zidebactam, cefepime-enmetazobactam, omadacycline, eravacycline, and comparator antibiotics against Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii complex causing bloodstream infection in Taiwan, 2020

OBJECTIVES

: To determine the in vitro activities of novel and comparator antibiotics against gram-negative bacteria (GNB) in Taiwan.

METHODS

: Isolates of Escherichia coli (n = 335), Klebsiella pneumoniae (n = 316; 144 isolates with hyperviscosity characteristics), Pseudomonas aeruginosa (n = 271), Acinetobacter baumannii complex species (n = 187), and non-typhoidal Salmonella species (n = 226), Shigella species (n = 13) from miscellaneous culture sources were collected in 2020 in Taiwan. The MICs of the isolates to test antibiotics were determined using the broth microdilution method. GeneXpert was used to detect genes encoding carbapenemases among the carbapenem-non-susceptible (NS) Enterobacterales isolates.

RESULTS

: The MIC values of the cefepime-enmetazobactam combination against extended-spectrum β-lactamase-producing E. coli and K. pneumoniae isolates (MIC₉₀ ≤ 0.5 mg/L), bla_KPC-harboring E. coli isolates (0.25 mg/L; n = 2), and 80% of bla_OXA-48-like gene-harboring K. pneumoniae isolates (≤2 mg/L) were low. The MIC ranges of the cefepime-zidebactam against carbapenemase-producing Enterobacterales isolates (irrespective of the carbapenemase type [MIC₉₀ ≤ 4 mg/L]) and carbapenem-NS or ceftolozane-tazobactam-NS P. aeruginosa isolates (MIC₉₀ value, 8 mg/L) were significantly lower than those of the cefepime-enmetazobactam.

CONCLUSIONS

: The efficacy of novel antibiotics against important drug-resistant GNB must be monitored and validated during the clinical treatment of patients.

Evaluation of the Therapeutic Outcomes of Antibiotic Regimen Against Carbapenemase-Producing Klebsiella pneumoniae: A Systematic Review and Meta-Analysis

Background: Carbapenemase-producing Klebsiella pneumoniae (CpKP) has been implicated as an increasing threat to public health. CpKP is a ubiquitous, opportunistic pathogen that causes both hospital and community acquired infections. This organism hydrolyzes carbapenems and other β-lactams and thus, leading to multiple resistance to these antibiotics. Despite the difficult to treat nature of infections caused by CpKP, little has been discussed on the mortality, clinical response and microbiological success rates associated with various antibiotic regimen against CpKP. This meta-analysis was designed to fill the paucity of information on the clinical impact of various antibiotic therapeutic regimens among patients infected with CpKP.

Materials and Methods: Literature in most English databases such as Medline through PubMed, Google Scholar, Web of Science, Cochrane Library and EMBASE, were searched for most studies published between the years 2015–2020. Data were analyzed using the R studio 2.15.2 statistical software program (metaphor and meta Package, Version 2) by random-effects (DerSimonian and Laird) model.

Results: Twenty-one (21) studies including 2841 patients who had been infected with CpKP were analysed. The overall mortality rate was 32.2% (95%CI = 26.23–38.87; I² = 89%; p-value ≤ 0.01, Number of patients = 2716). Pooled clinical and microbiological success rates were 67.6% (95%CI = 58.35–75.64, I² = 22%, p-value = 0.25, Number of patients = 171) and 74.9% (95%CI = 59.02–86.09, I² = 53%, p-value = 0.05, Number of patients = 121), respectively. CpKP infected patients treated with combination therapy are less likely to die as compared to those treated with monotherapy (OR = 0.55, 95%CI = 0.35–0.87, p-value = 0.01, Number of patients = 1,475). No significant difference existed between the mortality rate among 60years and above patients vs below 60years (OR = 0.84, 95%CI = 0.28–2.57, p-value = 0.76, 6 studies, Number of patients = 1,688), and among patients treated with triple therapy vs. double therapy (OR = 0.50, 95%CI = 0.21–1.22, p-value = 0.13, 2 studies, Number of patients = 102). When compared with aminoglycoside-sparing therapies, aminoglycoside-containing therapies had positive significant outcomes on both mortality and microbiological success rates.

Conclusion: New effective therapies are urgently needed to help fight infections caused by this organism. The effective use of various therapeutic options and the strict implementation of infection control measures are of utmost importance in order to prevent infections caused by CpKP. Strict national or international implementation of infection control measures and treatment guidelines will help improve healthcare, and equip governments and communities to respond to and prevent the spread of infectious diseases caused by CpKP.

Penetration of Antibacterial Agents into Pulmonary Epithelial Lining Fluid: An Update

A comprehensive review of drug penetration into pulmonary epithelial lining fluid (ELF) was previously published in 2011. Since then, an extensive number of studies comparing plasma and ELF concentrations of antibacterial agents have been published and are summarized in this review. The majority of the studies included in this review determined ELF concentrations of antibacterial agents using bronchoscopy and bronchoalveolar lavage, and this review focuses on intrapulmonary penetration ratios determined with area under the concentration-time curve from healthy human adult studies or pharmacokinetic modeling of various antibacterial agents. If available, pharmacokinetic/pharmacodynamic parameters determined from preclinical murine infection models that evaluated ELF concentrations are also provided. There are also a limited number of recently published investigations of intrapulmonary penetration in critically ill patients with lower respiratory tract infections, where greater variability in ELF concentrations may exist. The significance of these changes may impact the intrapulmonary penetration in the setting of infection, and further studies relating ELF concentrations to clinical response are needed. Phase I drug development programs now include assessment of initial pharmacodynamic target values for pertinent organisms in animal models, followed by evaluation of antibacterial penetration into the human lung to assist in dosage selection for clinical trials in infected patients. The recent focus has been on β-lactam agents, including those in combination with β-lactamase inhibitors, particularly due to the rise of multidrug-resistant infections. This manifests as a large portion of the review focusing on cephalosporins and carbapenems, with or without β-lactamase inhibitors, in both healthy adult subjects and critically ill patients with lower respiratory tract infections. Further studies are warranted in critically ill patients with lower respiratory tract infections to evaluate the relationship between intrapulmonary penetration and clinical and microbiological outcomes. Our clinical research experience with these studies, along with this literature review, has allowed us to outline key steps in developing and evaluating dosage regimens to treat extracellular bacteria in lower respiratory tract infections.

Management of Infections Caused by Multidrug-resistant Gram-negative Pathogens: Recent Advances and Future Directions

During the last decades, the isolation of multidrug-resistant Gram-negative (MDR-GN) bacteria has dramatically increased worldwide and has been associated with significant delays in the administration of adequate antibiotic treatment, resulting in increased morbidity and mortality rates. Given specific challenges to effective therapy with old antibiotics, there is the need to establish adequate clinical and therapeutic recommendations for antibiotic treatment of MDR-GN pathogens. Herein, we will review risk factors for harbouring infections due to MDR-GN bacteria, proposing an algorithm for the choice of empirical treatment when a MDR-GN pathogen is suspected. In addition, we will report our recommendations regarding the first- and second-line treatment options for hospitalized patients with serious infections caused by extended-spectrum β-lactamases producing Enterobacterales, carbapenem-resistant Enterobacterales, MDR Pseudomonas aeruginosa and MDR Acinetobacter baumannii. Recommendations have been specially focused, for each pathogen, on bloodstream infections, nosocomial pneumonia, and urinary tract infections.

Rational design of a new antibiotic class for drug-resistant infections

The development of new antibiotics to treat infections caused by drug-resistant Gram-negative pathogens is of paramount importance as antibiotic resistance continues to increase worldwide¹. Here we describe a strategy for the rational design of diazabicyclooctane inhibitors of penicillin-binding proteins from Gram-negative bacteria to overcome multiple mechanisms of resistance, including β-lactamase enzymes, stringent response and outer membrane permeation. Diazabicyclooctane inhibitors retain activity in the presence of β-lactamases, the primary resistance mechanism associated with β-lactam therapy in Gram-negative bacteria^2,3. Although the target spectrum of an initial lead was successfully re-engineered to gain in vivo efficacy, its ability to permeate across bacterial outer membranes was insufficient for further development. Notably, the features that enhanced target potency were found to preclude compound uptake. An improved optimization strategy leveraged porin permeation properties concomitant with biochemical potency in the lead-optimization stage. This resulted in ETX0462, which has potent in vitro and in vivo activity against Pseudomonas aeruginosa plus all other Gram-negative ESKAPE pathogens, Stenotrophomonas maltophilia and biothreat pathogens. These attributes, along with a favourable preclinical safety profile, hold promise for the successful clinical development of the first novel Gram-negative chemotype to treat life-threatening antibiotic-resistant infections in more than 25 years.

Old and New Beta-Lactamase Inhibitors: Molecular Structure, Mechanism of Action, and Clinical Use

The β-lactams have a central place in the antibacterial armamentarium, but the increasing resistance to these drugs, especially among Gram-negative bacteria, is becoming one of the major threats to public health worldwide. Treatment options are limited, and only a small number of novel antibiotics are in development. However, one of the responses to this threat is the combination of β-lactam antibiotics with β-lactamase inhibitors, which are successfully used in the clinic for overcoming resistance by inhibiting β-lactamases. The existing inhibitors inactivate most of class A and C serine β-lactamases, but several of class D and B (metallo-β-lactamase) are resistant. The present review provides the status and knowledge concerning current β-lactamase inhibitors and an update on research efforts to identify and develop new and more efficient β-lactamase inhibitors.

In vitro activity of imipenem/relebactam, meropenem/vaborbactam, ceftazidime/avibactam, cefepime/zidebactam and other novel antibiotics against imipenem-non-susceptible Gram-negative bacilli from Taiwan

OBJECTIVES

To investigate the susceptibility of imipenem-non-susceptible Escherichia coli (INS-EC), Klebsiella pneumoniae (INS-KP), Acinetobacter baumannii (INS-AB) and Pseudomonas aeruginosa (INS-PA) to novel antibiotics.

METHODS

MICs were determined using the broth microdilution method. Carbapenemase and ESBL phenotypic testing and PCR for genes encoding ESBLs, AmpCs and carbapenemases were performed.

RESULTS

Zidebactam, avibactam and relebactam increased the respective susceptibility rates to cefepime, ceftazidime and imipenem of 17 INS-EC by 58.8%, 58.8% and 70.6%, of 163 INS-KP by 77.9%, 88.3% and 76.1% and of 81 INS-PA by 45.7%, 38.3% and 85.2%, respectively. Vaborbactam increased the meropenem susceptibility of INS-EC by 41.2% and of INS-KP by 54%. Combinations of β-lactams and novel β-lactamase inhibitors or β-lactam enhancers (BLI-BLE) were inactive against 136 INS-AB. In 58 INS-EC and INS-KP with exclusively blaKPC-like genes, zidebactam, avibactam, relebactam and vaborbactam increased the susceptibility of the partner β-lactams by 100%, 96.6%, 84.5% and 75.9%, respectively. In the presence of avibactam, ceftazidime was active in an additional 85% of 20 INS-EC and INS-KP with exclusively blaOXA-48-like genes while with zidebactam, cefepime was active in an additional 75%. INS-EC and INS-KP with MBL genes were susceptible only to cefepime/zidebactam. The β-lactam/BLI-BLE combinations were active against INS-EC and INS-KP without detectable carbapenemases. For INS-EC, INS-KP and INS-AB, tigecycline was more active than omadacycline and eravacycline but eravacycline had a lower MIC distribution. Lascufloxacin and delafloxacin were active in <35% of these INS isolates.

CONCLUSIONS

β-Lactam/BLI-BLE combinations were active in a higher proportion of INS-EC, INS-KP and INS-PA. The susceptibility of novel fluoroquinolones and tetracyclines was not superior to that of old ones.

Microbiological Characterization of VNRX-5236, a Broad-Spectrum β-Lactamase Inhibitor for Rescue of the Orally Bioavailable Cephalosporin Ceftibuten as a Carbapenem-Sparing Agent against Strains of Enterobacterales Expressing Extended-Spectrum β-Lactamases and Serine Carbapenemases

There is an urgent need for oral agents to combat resistant Gram-negative pathogens. Here, we describe the characterization of VNRX-5236, a broad-spectrum boronic acid β-lactamase inhibitor (BLI), and its orally bioavailable etzadroxil prodrug, VNRX-7145. VNRX-7145 is being developed in combination with ceftibuten, an oral cephalosporin, to combat strains of Enterobacterales expressing extended-spectrum β-lactamases (ESBLs) and serine carbapenemases. VNRX-5236 is a reversible covalent inhibitor of serine β-lactamases, with inactivation efficiencies on the order of 10⁴ M⁻¹ · sec⁻¹, and prolonged active site residence times (t_1/2, 5 to 46 min). The spectrum of inhibition includes Ambler class A ESBLs, class C cephalosporinases, and class A and D carbapenemases (KPC and OXA-48, respectively). Rescue of ceftibuten by VNRX-5236 (fixed at 4 μg/ml) in isogenic strains of Escherichia coli expressing class A, C, or D β-lactamases demonstrated an expanded spectrum of activity relative to oral comparators, including investigational penems, sulopenem, and tebipenem. VNRX-5236 rescued ceftibuten activity in clinical isolates of Enterobacterales expressing ESBLs (MIC₉₀, 0.25 μg/ml), KPCs (MIC₉₀, 1 μg/ml), class C cephalosporinases (MIC₉₀, 1 μg/ml), and OXA-48-type carbapenemases (MIC₉₀, 1 μg/ml). Frequency of resistance studies demonstrated a low propensity for recovery of resistant variants at 4× the MIC of the ceftibuten/VNRX-5236 combination. In vivo, whereas ceftibuten alone was ineffective (50% effective dose [ED₅₀], >128 mg/kg), ceftibuten/VNRX-7145 administered orally protected mice from lethal septicemia caused by Klebsiella pneumoniae producing KPC carbapenemase (ED₅₀, 12.9 mg/kg). The data demonstrate potent, broad-spectrum rescue of ceftibuten activity by VNRX-5236 in clinical isolates of cephalosporin-resistant and carbapenem-resistant Enterobacterales.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

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.

An update on cefepime and its future role in combination with novel β-lactamase inhibitors for MDR Enterobacterales and Pseudomonas aeruginosa

Cefepime, a wide-spectrum β-lactam antibiotic, has been in use for the treatment of serious bacterial infections for almost 25 years. Since its clinical development, there has been a dramatic shift in its dosing, with 2 g every 8 hours being preferred for serious infections to optimize pharmacokinetic/pharmacodynamic considerations. The advent of ESBLs has become a threat to its ongoing use, although future coadministration with β-lactamase inhibitors (BLIs) under development is an area of intense study. There are currently four new cefepime/BLI combinations in clinical development. Cefepime/zidebactam is generally active against MBL-producing Enterobacterales and Pseudomonas aeruginosa, in vitro and in animal studies, and cefepime/taniborbactam has activity against KPC and OXA-48 producers. Cefepime/enmetazobactam and cefepime/tazobactam are potential carbapenem-sparing agents with activity against ESBLs. Cefepime/enmetazobactam has completed Phase III and cefepime/taniborbactam is in Phase III clinical studies, where they are being tested against carbapenems or piperacillin/tazobactam for the treatment of complicated urinary tract infections. While these combinations are promising, their role in the treatment of MDR Gram-negative infections can only be determined with further clinical studies.

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.

Treatment for carbapenem-resistant Enterobacterales infections: recent advances and future directions

Carbapenem-resistant Enterobacterales (CRE) are a growing threat to human health worldwide. CRE often carry multiple resistance genes that limit treatment options and require longer durations of therapy, are more costly to treat, and necessitate therapies with increased toxicities when compared with carbapenem-susceptible strains. Here, we provide an overview of the mechanisms of resistance in CRE, the epidemiology of CRE infections worldwide, and available treatment options for CRE. We review recentlyapproved agents for the treatment of CRE, including ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, and novel aminoglycosides and tetracyclines. We also discuss recent advances in phage therapy and antibiotics that are currently in development targeted to CRE. The potential for the development of resistance to these therapies remains high, and enhanced antimicrobial stewardship is imperative both to reduce the spread of CRE worldwide and to ensure continued access to efficacious treatment options.