Interaction of Avibactam with Class B Metallo-β-Lactamases

Rapid, culture-free detection of carbapenem-resistant Klebsiella pneumoniae in a case of bloodstream infection using genomics

Timely diagnosis and treatment of sepsis is a major challenge faced by critical care specialists around the world. The traditional blood culture methods have a significant turnaround time which delays targeted therapy leading to poor prognosis. In the current study, we highlight the clinical utility of a genomics solution for diagnosis and management of bloodstream infections by combining the real-time DNA sequencing of Oxford Nanopore Technology with an automated genomic data analysis software. We identify a carbapenem-resistant Klebsiella pneumoniae directly from a blood sample in <24 hours and thereby prove the effectiveness of the test in early diagnosis of sepsis.

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.

Prevalence and molecular characteristics of ceftazidime-avibactam resistance among carbapenem-resistant Pseudomonas aeruginosa clinical isolates

OBJECTIVES

Resistance against ceftazidime-avibactam (CZA) in carbapenem-resistant Pseudomonas aeruginosa (CRPA) is emerging. This study was aimed at detecting the prevalence and molecular characteristics of CZA-resistant CRPA clinical isolates in Guangdong Province, China.

METHODS

The antimicrobial susceptibility profile of these strains was determined. A subset of 16 CZA-resistant CRPA isolates was analysed by whole-genome sequencing (WGS). Genetic surroundings of carbapenem resistance genes and pan-genome-wide association analysis were further studied.

RESULTS

Of the 250 CRPA isolates, CZA resistance rate was 6.4% (16/250). The minimum inhibitory concentration (MIC) of CZA range was from 0.25 to >256 mg/L. MIC50 and MIC90 were 2/4 and 8/4 mg/L, respectively. Among the 16 CZA-resistant CRPA strains, 31.3% (5/16) of them carried class B carbapenem resistance genes, including blaIMP-4, blaIMP-45, and blaVIM-2, located on IncP-2 megaplasmids or chromosomes, respectively. Pan-genome-wide association analysis of accessory genes for CZA-susceptible or -resistant CRPA isolates showed that PA1874, a hypothetical protein containing BapA prefix-like domain, was enriched in CZA-resistant group significantly.

CONCLUSIONS

Class B carbapenem resistance genes play important roles in CZA resistance. Meanwhile, the PA1874 gene may be a novel mechanism involving in CZA resistance. It is necessary to continually monitor CZA-resistant CRPA isolates.

In Vitro Susceptibility to Ceftazidime-Avibactam and Comparator Antimicrobial Agents of Carbapenem-Resistant Enterobacterales Isolates

The emergence of carbapenem-resistant Enterobacterales (CRE) has been recognized as a significant concern globally. Ceftazidime/avibactam (CZA) is a novel β-lactam/β-lactamase inhibitor that has demonstrated activity against isolates producing class A, C, and D β-lactamases. Here-in, we evaluated the in vitro activity of CZA and comparator antimicrobial agents against 858 CRE isolates, arising from the Southeast Asian region, collected from a large tertiary hospital in Singapore. These CRE isolates mainly comprised Klebsiella pneumoniae (50.5%), Escherichia coli (29.4%), and Enterobacter cloacae complex (17.1%). Susceptibility rates to levofloxacin, imipenem, meropenem, doripenem, aztreonam, piperacillin/tazobactam, cefepime, tigecycline, and polymyxin B were low. CZA was the most active β-lactam agent against 68.9% of the studied isolates, while amikacin was the most active agent among all comparator antibiotics (80% susceptibility). More than half of the studied isolates (51.4%) identified were Klebsiella pneumoniae carbapenemase (KPC)-2 producers, 25.9% were New Delhi metallo-β-lactamase (NDM) producers, and Oxacillinase (OXA)-48-like producers made up 10.7%. CZA was the most active β-lactam agent against KPC-2, OXA-48-like, and Imipenemase (IMI) producers (99.3% susceptible; MIC50/90: ≤1/2 mg/L). CZA had excellent activity against the non-carbapenemase-producing CRE (91.4% susceptible; MIC50/90: ≤1/8 mg/L). Expectedly, CZA had no activity against the metallo-β-lactamases (MBL)-producing CRE (NDM- and Imipenemase MBL (IMP) producers; 27.2% isolates), and the carbapenemase co-producing CRE (NDM + KPC, NDM + OXA-48-like, NDM + IMP; 3.0% isolates). CZA is a promising addition to our limited armamentarium against CRE infections, given the reasonably high susceptibility rates against these CRE isolates. Careful stewardship and rational dosing regimens are required to preserve CZA's utility against CRE infections.

In vitro activity of cefiderocol against MBL-producing Gram-negative bacteria collected in North America and Europe in five consecutive annual multinational SIDERO-WT surveillance studies (2014-2019)

OBJECTIVES

To evaluate the in vitro antibacterial activity of cefiderocol, a siderophore cephalosporin against MBL-producing clinical isolates.

METHODS

MBL-producing strains were selected from clinical isolates of Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii complex collected in North America and Europe in five consecutive annual multinational SIDERO-WT surveillance studies from 2014 to 2019. MICs of cefiderocol and comparator agents were determined by the broth microdilution method according to the CLSI guideline.

RESULTS

A total of 452 MBL-producing strains consisting of 200 Enterobacterales, 227 P. aeruginosa and 25 A. baumannii complex were identified. The highest number of MBL-producing Enterobacterales strains were detected in Greece. MBL-producing strains of both P. aeruginosa and A. baumannii complex were isolated most frequently in Russia. For Enterobacterales, 91.5% or 67.5% of MBL-producing strains had cefiderocol MIC values ≤4 mg/L (CLSI susceptibility breakpoint) or ≤2 mg/L (EUCAST susceptibility breakpoint), respectively. All MIC values of cefiderocol for MBL-producing P. aeruginosa strains were ≤4 mg/L (CLSI susceptibility breakpoint), and 97.4% of them had cefiderocol MIC values ≤2 mg/L (EUCAST susceptibility breakpoint). For A. baumannii complex, 60.0% or 44.0% of MBL-producing strains had cefiderocol MIC values ≤4 mg/L (CLSI susceptibility breakpoint) or ≤2 mg/L (EUCAST pharmacokinetic-pharmacodynamic susceptibility breakpoint), respectively. Against all types of MBL-producing strains, MIC distribution curves of cefiderocol were located in the lowest numerical values, compared with other β-lactams and β-lactam/β-lactamase inhibitor combinations tested and ciprofloxacin.

CONCLUSIONS

Although the types of MBL-producing strains isolated by country varied, cefiderocol showed potent in vitro activity against all types of MBL-producing Gram-negative bacteria regardless of the bacterial species.

Metallo-β-lactamase-mediated antimicrobial resistance and progress in inhibitor discovery

Resistance to β-lactam antibiotics is rapidly growing, substantially due to the spread of serine-β-lactamases (SBLs) and metallo-β-lactamases (MBLs), which efficiently catalyse β-lactam hydrolysis. Combinations of a β-lactam antibiotic with an SBL inhibitor have been clinically successful; however, no MBL inhibitors have been developed for clinical use. MBLs are a worrying resistance vector because they catalyse hydrolysis of all β-lactam antibiotic classes, except the monobactams, and they are being disseminated across many bacterial species worldwide. Here we review the classification, structures, substrate profiles, and inhibition mechanisms of MBLs, highlighting current clinical problems due to MBL-mediated resistance and progress in understanding and combating MBL-mediated resistance.

The primary pharmacology of ceftazidime/avibactam: resistance in vitro

This article reviews resistance to ceftazidime/avibactam as an aspect of its primary pharmacology, linked thematically with recent reviews of the basic in vitro and in vivo translational biology of the combination (J Antimicrob Chemother 2022; 77: 2321-40 and 2341-52). In Enterobacterales or Pseudomonas aeruginosa, single-step exposures to 8×  MIC of ceftazidime/avibactam yielded frequencies of resistance from <∼0.5 × 10-9 to 2-8 × 10-9, depending on the host strain and the β-lactamase harboured. β-Lactamase structural gene mutations mostly affected the avibactam binding site through changes in the Ω-loop: e.g. Asp179Tyr (D179Y) in KPC-2. Other mutations included ones proposed to reduce the permeability to ceftazidime and/or avibactam through changes in outer membrane structure, up-regulated efflux, or both. The existence, or otherwise, of cross-resistance between ceftazidime/avibactam and other antibacterial agents was also reviewed as a key element of the preclinical primary pharmacology of the new agent. Cross-resistance between ceftazidime/avibactam and other β-lactam-based antibacterial agents was caused by MBLs. Mechanism-based cross-resistance was not observed between ceftazidime/avibactam and fluoroquinolones, aminoglycosides or colistin. A low level of general co-resistance to ceftazidime/avibactam was observed in MDR Enterobacterales and P. aeruginosa. For example, among 2821 MDR Klebsiella spp., 3.4% were resistant to ceftazidime/avibactam, in contrast to 0.07% of 8177 non-MDR isolates. Much of this was caused by possession of MBLs. Among 1151 MDR, XDR and pandrug-resistant isolates of P. aeruginosa from the USA, 11.1% were resistant to ceftazidime/avibactam, in contrast to 3.0% of 7452 unselected isolates. In this case, the decreased proportion susceptible was not due to MBLs.

Multidrug-resistant Gram-negative bacilli recovered from respiratory and blood specimens from adults: the ATLAS surveillance program in European hospitals, 2018-2020

The population of people ≥65 years of age is increasing in Europe. Pneumonia is a prominent cause of infection in this age group. These patients may be at heightened risk of infection caused by multidrug-resistant (MDR) organisms owing to their frequent and prolonged contact with healthcare facilities as well as frequent exposure to antimicrobials and medical devices. However, ATLAS surveillance data did not demonstrate any difference in the incidence of MDR Gram-negative pathogens among patients ≥65 years of age and those aged <65 years. Higher rates of carbapenem-resistant Enterobacterales (CRE) and MDR Pseudomonas aeruginosa were observed in patients aged 18-64 years (10.7% and 32.3%, respectively) than in patients aged ≥65 years (5.0% and 25.4%, respectively). Significant therapeutic gaps were identified for CRE, carbapenem-resistant Acinetobacter baumannii (65.9% of isolates tested) and MDR P. aeruginosa, which continue to be prevalent in European hospitals. Among the antimicrobials evaluated, only colistin provided >75% in vitro coverage for these pathogens.

Evaluation of Dilution Susceptibility Testing Methods for Aztreonam in Combination with Avibactam against Enterobacterales

As multidrug and pan-resistance among Enterobacterales continue to increase, there is an urgent need for more therapeutic options to treat these infections. New β-lactam and β-lactam inhibitor (BLI) combinations have a broad spectrum of activity, but those currently approved do not provide coverage against isolates harboring metallo-β-lactamases (MBL). Aztreonam (ATM) and avibactam (AVI) in combination (ATM/AVI; AVI at 4 μg/mL fixed concentration) provides a similarly broad range of activity while maintaining activity against MBL-producing isolates. The in vitro susceptibility testing of ATM/AVI by standard methods was evaluated during development. This study investigated the impact of nonstandard testing conditions on the activity of ATM/AVI as observed during broth microdilution testing as well as the equivalency between agar dilution and broth microdilution MIC values when testing a diverse panel of Enterobacterales (N = 201). Nonstandard test conditions evaluated included inoculum density, atmosphere of incubation, media pH, varied medium cation concentrations, incubation time, varied serum concentrations, testing in pooled urine instead of media, addition of blood to the media, and the presence of surfactant. Generally, apart from low pH and high inoculum density, nonstandard testing parameters did not affect ATM/AVI broth microdilution MIC values. Correlation of MIC values obtained by agar dilution and broth microdilution resulted in an essential agreement of 97.0% for all tested Enterobacterales. Variation of standard testing conditions had little impact on broth microdilution MIC values for ATM/AVI. The correlation between broth microdilution and agar dilution MICs suggests both methods are reliable for determination of ATM/AVI MIC values. IMPORTANCE Increasing antibiotic resistance and emergence of pan-resistant isolates threaten the ability to control infections and to provide many other medical interventions such as surgery and chemotherapy, among others. New therapies are required to control emerging resistance mechanisms, including the increase in metallo-β-lactamases. Some new antibiotic combinations provide coverage against highly resistant isolates but are unable to target organisms that produce metallo-β-lactamases. Aztreonam in combination with avibactam provides a broad spectrum of activity against highly resistant isolates that also targets metallo-β-lactamase-producing organisms. An important part of drug development is the ability for clinical labs to determine the susceptibility of isolates to the antimicrobial. This manuscript investigates the in vitro susceptibility testing of aztreonam/avibactam with nonstandard testing conditions and a correlation study between broth microdilution and agar dilution against clinical isolates encoding a variety of resistance mechanisms. Overall, aztreonam/avibactam was generally unaffected by changes in testing conditions and showed strong agar/broth correlation.

Genomic Analysis of Ceftazidime/Avibactam-Resistant GES-Producing Sequence Type 235 Pseudomonas aeruginosa Isolates

The emergence of ceftazidime/avibactam (CZA) resistance among Guiana extended-spectrum β-lactamase (GES)-producing Pseudomonas aeruginosa isolates has rarely been described. Herein, we analyze the phenotypic and genomic characterization of CZA resistance in different GES-producing P. aeruginosa isolates that emerged in our institution. A subset of nine CZA-resistant P. aeruginosa isolates was analyzed and compared with thirteen CZA-susceptible isolates by whole-genome sequencing (WGS). All CZA-resistant isolates belonged to the ST235 clone and O11 serotype. A variety of GES enzymes were detected: GES-20 (55.6%, 5/9), GES-5 (22.2%, 2/9), GES-1 (11.1%, 1/9), and GES-7 (11.1%, 1/9). WGS revealed the presence of two mutations within the bla_GES-20 gene comprising two single-nucleotide substitutions, which caused aspartic acid/serine and leucine/premature stop codon amino acid changes at positions 165 (D165S) and 237 (L237X), respectively. No major differences in the mutational resistome (AmpC, OprD porin, and MexAB-OprM efflux pump-encoding genes) were found among CZA-resistant and CZA-susceptible isolates. None of the mutations that have been previously demonstrated to cause CZA resistance were observed. Different mutations within the bla_GES-20 gene were documented in CZA-resistant GES-producing P. aeruginosa isolates belonging to the ST235 clone in our institution. Although further analysis should be performed, according to our results, other resistance mechanisms might be involved in CZA resistance.

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).

Differences in the Distribution of Species, Carbapenemases, Sequence Types, Antimicrobial Heteroresistance and Mortality Rates Between Pediatric and Adult Carbapenemase-Producing Enterobacterales in Bloodstream Infections

The dissemination of carbapenemase-producing Enterobacterales (CPE) is worrisome given their scarce treatment options. CPE bloodstream infections (BSIs) had a high mortality rate in adults, and there was little data on pediatric CPE-BSIs around the world. We comprehensively explored the differences in the clinical and microbiological characteristics between pediatric and adult CPE-BSIs. Forty-eight pediatric and 78 adult CPE-BSIs cases were collected. All-cause 30 day-mortality in children with CPE-BSIs (14.6%, 7/48) was significantly lower than that in adult patients (42.3%, 33/78, p = 0.001). The subgroup in adults empirically treated with tigecycline as an active drug displayed a significantly higher 30-days crude mortality (63.3%, 19/30) than the subgroup treated without tigecycline (29.2%, 14/48, p = 0.003). K. pneumoniae was the most prevalent species in both the pediatric (45.8%, 22/48) and adult populations (64.1%, 50/78), with discrepant carbapenemase genes in each population: 95.4% (21/22) of the pediatric K. pneumoniae isolates carried bla_NDM, while 82.0% (41/50) of the adult strains harbored bla_KPC. The ratio of E. coli in children (37.5%) was significantly higher than that in adults (12.8%, p = 0.002). In both populations, the majority of E. coli expressed bla_NDM, particularly bla_NDM−5. With statistical significance, bla_NDM was much more common in children (95.8%, 46/48) than in adults (34.6%, 27/78). The rate of multiple-heteroresistance phenotypes in children was as high as 87.5%, which was much lower in adults (57.1%). Agar dilution checkboard experiment against one pediatric carbapenemase-producing E. coli isolates showed that the combination of amikacin and fosfomycin yielded an additive effect. Overall, K. pneumoniae was the most common CPE-BSIs pathogen in both populations, with NDM-producing K. pneumoniae and KPC-producing ST11 K. pneumoniae being the most prevalent species in children and adults, respectively. E. coli was more prevalent in children than in adults, yet bla_NDM−5 was the most common carbapenem-resistant mechanism in E. coli in both populations. The wide range of multiple-heteroresistance combination traits found in different pathogen species from different host populations should provide a good foundation for future combination therapy design. Further investigations from more CPE isolates of various species are needed to evaluate the possible in vitro partial synergy of the amikacin and fosfomycin combination.

Pseudomonas aeruginosa Pneumonia: Evolution of Antimicrobial Resistance and Implications for Therapy

Pseudomonas aeruginosa (PA), a non-lactose-fermenting gram-negative bacillus, is a common cause of nosocomial infections in critically ill or debilitated patients, particularly ventilator-associated pneumonia (VAP), and infections of urinary tract, intra-abdominal, wounds, skin/soft tissue, and bloodstream. PA rarely affects healthy individuals, but may cause serious infections in patients with chronic structural lung disease, comorbidities, advanced age, impaired immune defenses, or with medical devices (e.g., urinary or intravascular catheters, foreign bodies). Treatment of pseudomonal infections is difficult, as PA is intrinsically resistant to multiple antimicrobials, and may acquire new resistance determinants even while on antimicrobial therapy. Mortality associated with pseudomonal VAP or bacteremias is high (> 35%) and optimal therapy is controversial. Over the past three decades, antimicrobial resistance (AMR) among PA has escalated globally, via dissemination of several international multidrug resistant "epidemic" clones. We discuss the importance of PA as a cause of pneumonia including health care-associated pneumonia, hospital-acquired pneumonia, VAP, the emergence of AMR to this pathogen, and approaches to therapy (both empirical and definitive).

Targeting Metalloenzymes by Boron-Containing Metal-Binding Pharmacophores

Metalloenzymes have critical roles in a wide range of biological processes and are directly involved in many human diseases; hence, they are considered as important targets for therapeutic intervention. The specific characteristics of metal ion(s)-containing active sites make exploitation of metal-binding pharmacophores (MBPs) critical to inhibitor development targeting metalloenzymes. This Perspective focuses on boron-containing MBPs, which display unique binding modes with metalloenzyme active sites, particularly via mimicking native substrates or tetrahedral transition states. The design concepts regarding boron-containing MBPs are highlighted through the case analyses on five distinct classes of clinically relevant nucleophilic metalloenzymes from medicinal chemistry perspectives. The challenges (e.g., selectivity) faced by some boron-containing MBPs and possible strategies (e.g., bioisosteres) for metalloenzyme inhibitor transformation are also discussed.

In Vitro Activity of Auranofin in Combination With Aztreonam-Avibactam Against Metallo-β-lactamase (MBL)-Producing Enterobacterales

Objectives

To assess the efficacy of aztreonam-avibactam-auranofin (ATM-AVI-AUR) against a collection of 88 carbapenemase-producing Enterobacterales (CPE) clinical isolates and 6 in vitro selected ATM-AVI-resistant CPE with CMY-16 Tyr150Ser and Asn346His mutants or transformants.

Methods

MICs of imipenem, ceftazidime-avibact8am (CAZ-AVI), ATM-AVI, CAZ-AVI-AUR and ATM-AVI-AUR were determined via the broth microdilution method. Genetic background and carbapenemase genes were determined by PCR and Sanger sequencing.

Results

AUR alone showed little antibacterial activity with AUR MICs were greater than 64 μg/mL for all the 88 clinical CPE isolates. The addition of AUR (16 μg/mL) resulted in an 3-folding dilutions MIC reduction of ATM-AVI MIC₅₀ (0.5 to 0.0625 μg/mL) and a 2-folding dilutions MIC reduction of MIC₉₀ (1 to 0.25 μg/mL) against all 88 clinical CPE isolates, respectively. Notably, the reduced ATM-AVI MIC values were mainly found in MBL-producers, and the MIC₅₀ and MIC₉₀ reduced by 2-folding dilutions (0.25 to 0.0625 μg/mL) and 3-folding dilutions (2 to 0.25 μg/mL) respectively by AUR among the 51 MBL-producers. By contrast, the addition of AUR did not showed significant effects on ATM-AVI MIC₅₀ (0.0625 μg/mL) and MIC₉₀ (0.125 μg/mL) among single KPC-producers. Interestingly, the addition of AUR restored the ATM-AVI susceptibility against the 6 in vitro selected ATM-AVI-resistant CMY-16 Tyr150Ser and Asn346His mutants or transfromants, with the MICs reduced from ≥32 μg/mL (32->256 μg/mL) to ≤8 μg/mL (0.0625-8 μg/mL).

Conclusions

Our results demonstrated that AUR potentiated the activities of CAZ-AVI and ATM-AVI against MBL-producing isolates in vitro. Importantly, AUR restored the ATM-AVI activity against ATM-AVI resistant mutant strains. As a clinically approved drug, AUR might be repurposed in combination with ATM-AVI to treat infections caused by highly resistant MBL-producing Enterobacterales.

In vitro activity of ceftazidime-avibactam and comparators against bacterial isolates collected in South Korea as part of the ATLAS global surveillance program (2016-2018)

Overall, 1,277 Enterobacterales and 296 P. aeruginosa isolates were collected in South Korea between 2016 and 2018. Rates of susceptibility were >95% to ceftazidime-avibactam, tigecycline, meropenem and amikacin among the Enterobacterales and of the P. aeruginosa collected, 92.9% were susceptibility to amikacin and 92.6% to ceftazidime-avibactam.

N-Aryl mercaptoacetamides as potential multi-target inhibitors of metallo-β-lactamases (MBLs) and the virulence factor LasB from Pseudomonas aeruginosa

Increasing antimicrobial resistance is evolving to be one of the major threats to public health. To reduce the selection pressure and thus to avoid a fast development of resistance, novel approaches aim to target bacterial virulence instead of growth. Another strategy is to restore the activity of antibiotics already in clinical use. This can be achieved by the inhibition of resistance factors such as metallo-β-lactamases (MBLs). Since MBLs can cleave almost all β-lactam antibiotics, including the “last resort” carbapenems, their inhibition is of utmost importance. Here, we report on the synthesis and in vitro evaluation of N-aryl mercaptoacetamides as inhibitors of both clinically relevant MBLs and the virulence factor LasB from Pseudomonas aeruginosa. All tested N-aryl mercaptoacetamides showed low micromolar to submicromolar activities on the tested enzymes IMP-7, NDM-1 and VIM-1. The two most promising compounds were further examined in NDM-1 expressing Klebsiella pneumoniae isolates, where they restored the full activity of imipenem. Together with their LasB-inhibitory activity in the micromolar range, this class of compounds can now serve as a starting point for a multi-target inhibitor approach against both bacterial resistance and virulence, which is unprecedented in antibacterial drug discovery.

Simultaneous inhibition of metallo-β-lactamases (MBLs) and virulence factors such as LasB from Pseudomonas aeruginosa offers a new approach to combat antibiotic-resistant pathogens.

Review of Ceftazidime-Avibactam for the Treatment of Infections Caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes a range of serious infections that are often challenging to treat, as this pathogen can express multiple resistance mechanisms, including multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes. Ceftazidime–avibactam is a combination antimicrobial agent comprising ceftazidime, a third-generation semisynthetic cephalosporin, and avibactam, a novel non-β-lactam β-lactamase inhibitor. This review explores the potential role of ceftazidime–avibactam for the treatment of P. aeruginosa infections. Ceftazidime–avibactam has good in vitro activity against P. aeruginosa relative to comparator β-lactam agents and fluoroquinolones, comparable to amikacin and ceftolozane–tazobactam. In Phase 3 clinical trials, ceftazidime–avibactam has generally demonstrated similar clinical and microbiological outcomes to comparators in patients with complicated intra-abdominal infections, complicated urinary tract infections or hospital-acquired/ventilator-associated pneumonia caused by P. aeruginosa. Although real-world data are limited, favourable outcomes with ceftazidime–avibactam treatment have been reported in some patients with MDR and XDR P. aeruginosa infections. Thus, ceftazidime–avibactam may have a potentially important role in the management of serious and complicated P. aeruginosa infections, including those caused by MDR and XDR strains.

In vitro activity of ceftazidime/avibactam and comparators against carbapenemase-producing Enterobacterales and Pseudomonas aeruginosa isolates collected globally between 2016 and 2018

OBJECTIVES

This study reports the antimicrobial activity of ceftazidime/avibactam (CZA) and comparators against carbapenemase-producing Enterobacterales (N = 1992) and carbapenemase-producing Pseudomonas aeruginosa (N = 784) collected in Africa/Middle East, Asia/South Pacific, Europe and Latin America (2016-2018).

METHODS

Minimum inhibitory concentrations (MICs) and susceptibility were determined using broth microdilution methodology and EUCAST breakpoints. Carbapenemase-encoding genes were detected using multiplex PCR.

RESULTS

No isolates of carbapenemase-producing, metallo-β-lactamase (MBL)-negative Enterobacterales from Africa/Middle East or Latin America were resistant to CZA; resistance rates in Europe and Asia/South Pacific were ≤4.5%. Colistin had the lowest resistance rate among MBL-positive isolates (6.0-11.4%). Enterobacterales isolates collected in Latin America predominantly carried a KPC carbapenemase (77.6%), whereas in Africa/Middle East OXA-48-like carbapenemases were most frequently detected (55.9%), and in Asia/South Pacific most isolates carried NDM carbapenemases (56.2%). Among all Enterobacterales carrying KPC carbapenemases, the lowest rate of resistance was to CZA (1.5%), and among isolates carrying NDM carbapenemases it was to colistin (10.8%). Among carbapenemase-producing, MBL-negative P. aeruginosa, resistance rates to CZA were 8.6% for isolates collected in Europe and 53.2% in Latin America. Isolates in each region most frequently carried VIM carbapenemases, ranging from 41.7% of isolates in Asia/South Pacific to 86.2% in Africa/Middle East. No P. aeruginosa carrying KPC or NDM carbapenemases and 1.0% of isolates carrying GES carbapenemases were resistant to colistin.

CONCLUSION

Given the limited therapeutic options to treat infections caused by carbapenemase-positive Enterobacterales and P. aeruginosa, continued surveillance of CZA activity as well as agents such as colistin is crucial.

Rapid personalized AMR diagnostics using two-dimensional antibiotic resistance profiling strategy employing a thermometric NDM-1 biosensor

Antimicrobial resistance (AMR) threatens global public health and modern surgical medicine. Expression of β-lactamase genes is the major mechanism by which pathogens become antibiotic resistant. Pathogens expressing extended spectrum β-lactamases (ESBL) and carbapenemases (CP) are especially difficult to treat and are associated with increased hospitalization and mortality rates. Despite considerable effort, identification of ESBLs and CPs in a clinically relevant timeframe remains challenging. In this study, a two-dimensional AMR profiling assay strategy was developed employing panels of antibiotics (penicillins, cephamycins, oximino-cephalosporins and carbapenems) and β-lactamases inhibitors (avibactam and EDTA). The assay required the development of a novel biosensor that employed New Delhi metallo-β-lactamase-1 (NDM-1) as the sensing element. Functionally probing β-lactamase activity using substrates and inhibitors combinatorically increased the informational content that enabled the development of assays capable of simultaneous, differential identification of multiple β-lactamases expressed in a single bacterial isolate. More specifically, the assay enabled the simultaneous identification of ESBL and CP in mock samples, as well as in an engineered construct which co-expressed these β-lactamases. The NDM-1 biosensor assay was 16 times and 8 times more sensitive than the ESBL Nordmann/Dortet/Poirel (NDP) and Carba Nordmann/Poirel (NP) assays, respectively. In a retrospective study, NDM-1 biosensor assays were able to differentially identify ESBLs, metallo-CPs and serine-CPs β-lactamases in 23 clinical isolates with 100% accuracy. An assay algorithm was developed which accelerated data analytics reducing turnaround to <1 h. The assay strategy integrated with AI-based data analytics has the potential to provide physicians with a comprehensive readout of patient AMR status.

In vitro antimicrobial susceptibility of clinical respiratory isolates to ceftazidime-avibactam and comparators (2016-2018)

BACKGROUND

This antimicrobial surveillance study reports in vitro antimicrobial activity and susceptibility data for a panel of agents against respiratory isolates of Enterobacterales and Pseudomonas aeruginosa.

METHODS

Isolates from respiratory specimens were collected in Africa/Middle East, Asia/South Pacific, Europe and Latin America between 2016 and 2018, as part of the Antimicrobial Testing Leadership and Surveillance (ATLAS) program. Broth microdilution methodology was used to quantify minimum inhibitory concentrations, from which rates of susceptibility were determined using EUCAST breakpoints (version 10). Rates of subsets with genes encoding β-lactamases (extended-spectrum β-lactamases [ESBLs], serine carbapenemases and metallo-β-lactamases [MBLs]) were also determined, as well as rates of multidrug-resistant (MDR) P. aeruginosa.

RESULTS

Among all respiratory Enterobacterales isolates, susceptibility to ceftazidime-avibactam, meropenem, colistin and amikacin was ≥94.4% in each region. For Enterobacterales isolates that were ESBL-positive or carbapenemase-positive/MBL-negative, ceftazidime-avibactam susceptibility was 93.6 and 98.9%, respectively. Fewer than 42.7% of MBL-positive Enterobacterales isolates were susceptible to any agents, except colistin (89.0% susceptible). Tigecycline susceptibility was ≥90.0% among Citrobacter koseri and Escherichia coli isolates, including all β-lactamase-positive subsets. ESBL-positive Enterobacterales were more commonly identified in each region than isolates that were ESBL/carbapenemase-positive; carbapenemase-positive/MBL-negative; or MBL-positive. Among all respiratory P. aeruginosa isolates, the combined susceptibility rates (susceptible at standard dosing regimen plus susceptible at increased exposure) were highest to ceftazidime-avibactam, colistin and amikacin (≥82.4% in each region). Susceptibility to colistin was ≥98.1% for all β-lactamase-positive subsets of P. aeruginosa. The lowest rates of antimicrobial susceptibility were observed among MBL-positive isolates of P. aeruginosa (≤56.6%), with the exception of colistin (100% susceptible). MDR P. aeruginosa were most frequently identified in each region (18.7-28.7%), compared with the subsets of ESBL-positive; carbapenemase-positive/MBL-negative; or MBL-positive isolates.

CONCLUSIONS

Rates of susceptibility among the collections of respiratory Enterobacterales and P. aeruginosa isolates were highest to ceftazidime-avibactam, colistin and amikacin in each region. Tigecycline was active against all subsets of C. koseri and E. coli, and colistin was active against all subsets of P. aeruginosa. The findings of this study indicate the need for continued antimicrobial surveillance among respiratory Gram-negative pathogens, in particular those with genes encoding MBLs.

Fragment-based screening and hit-based substructure search: Rapid discovery of 8-hydroxyquinoline-7-carboxylic acid as a low-cytotoxic, nanomolar metallo β-lactamase inhibitor

Metallo-β-lactamases (MBLs) are zinc-containing carbapenemases that inactivate a broad range of β-lactam antibiotics. There is a lack of β-lactamase inhibitors for restoring existing β-lactam antibiotics arsenals against common bacterial infections. Fragment-based screening of a non-specific metal chelator library demonstrates 8-hydroxyquinoline as a broad-spectrum nanomolar inhibitor against VIM-2 and NDM-1. A hit-based substructure search provided an early structure-activity relationship of 8-hydroxyquinolines and identified 8-hydroxyquinoline-7-carboxylic acid as a low-cytotoxic β-lactamase inhibitor that can restore β-lactam activity against VIM-2-expressing E. coli. Molecular modeling further shed structural insight into its potential mode of binding within the dinuclear zinc active site. 8-Hydroxyquinoline-7-carboxylic acid is highly stable in human plasma and human liver microsomal study, making it an ideal lead candidate for further development.

Structural Basis of Metallo-β-lactamase Inhibition by N-Sulfamoylpyrrole-2-carboxylates

Metallo-β-lactamases (MBLs) can efficiently catalyze the hydrolysis of all classes of β-lactam antibiotics except monobactams. While serine-β-lactamase (SBL) inhibitors (e.g., clavulanic acid, avibactam) are established for clinical use, no such MBL inhibitors are available. We report on the synthesis and mechanism of inhibition of N-sulfamoylpyrrole-2-carboxylates (NSPCs) which are potent inhibitors of clinically relevant B1 subclass MBLs, including NDM-1. Crystallography reveals that the N-sulfamoyl NH2 group displaces the dizinc bridging hydroxide/water of the B1 MBLs. Comparison of crystal structures of an NSPC and taniborbactam (VRNX-5133), presently in Phase III clinical trials, shows similar binding modes for the NSPC and the cyclic boronate ring systems. The presence of an NSPC restores meropenem efficacy in clinically derived E. coli and K. pneumoniae blaNDM-1. The results support the potential of NSPCs and related compounds as efficient MBL inhibitors, though further optimization is required for their clinical development.

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.

In Vitro Activity of a Novel Siderophore-Cephalosporin LCB10-0200 (GT-1), and LCB10-0200/Avibactam, against Carbapenem-Resistant Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa Strains at a Tertiary Hospital in Korea

The siderophore-antibiotic conjugate LCB10-0200 (a.k.a. GT-1) has been developed to combat multidrug-resistant Gram-negative bacteria. In this study, the in vitro activity of LCB10-0200 and LCB10-0200/avibactam (AVI) has been investigated against carbapenem-resistant Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. Minimal inhibitory concentrations (MICs) of LCB10-0200, LCB10-0200/AVI, aztreonam, aztreonam/AVI, ceftazidime, ceftazidime/AVI, and meropenem were measured using the agar dilution method. Whole genome sequencing was performed using Illumina and the resistome was analyzed. LCB10-0200 displayed stronger activity than the comparator drugs in meropenem-resistant E. coli and K. pneumoniae, and the addition of AVI enhanced the LCB10-0200 activity to MIC ≤ 0.12 mg/L for 90.5% of isolates. In contrast, whereas LCB10-0200 alone showed potent activity against meropenem-resistant A. baumannii and P. aeruginosa at MIC ≤ 4 mg/L for 84.3% of isolates, the combination with AVI did not improve its activity. LCB10-0200/AVI was active against CTX-M-, SHV-, CMY-, and KPC- producing E. coli and K. pneumoniae, while LCB10-0200 alone was active against ADC-, OXA-, and VIM- producing A. baumannii and P. aeruginosa. Both LCB10-0200 and LCB10-0200/AVI displayed low activity against IMP- and NDM- producing strains. LCB10-0200 alone exhibited strong activity against selected strains. The addition of AVI significantly increased LCB10-0200 activity against carbapenem-resistant E. coli, K. pneumoniae.

Assessing the Potency of β-Lactamase Inhibitors with Diverse Inactivation Mechanisms against the PenA1 Carbapenemase from Burkholderia multivorans

Burkholderia cepacia complex (Bcc) poses a serious health threat to people with cystic fibrosis or compromised immune systems. Infections often arise from Bcc strains, which are highly resistant to many classes of antibiotics, including β-lactams. β-Lactam resistance in Bcc is conferred largely via PenA-like β-lactamases. Avibactam was previously shown to be a potent inactivator of PenA1. Here, we examined the inactivation mechanism of PenA1, a class A serine carbapenemase from Burkholderia multivorans using β-lactamase inhibitors (β-lactam-, diazabicyclooctane-, and boronate-based) with diverse mechanisms of action. In whole cell based assays, avibactam, relebactam, enmetazobactam, and vaborbactam restored susceptibility to piperacillin against PenA1 expressed in Escherichia coli. The rank order of potency of inactivation in vitro based on k_inact/K_I or k₂/K values (range: 3.4 × 10² to 2 × 10⁶ M^-1 s^-1) against PenA1 was avibactam > enmetazobactam > tazobactam > relebactam > clavulanic acid > vaborbactam. The contribution of selected amino acids (S70, K73, S130, E166, N170, R220, K234, T237, and D276) in PenA1 toward inactivation was evaluated using site-directed mutagenesis. The S130A, R220A, and K234A variants of PenA1 were less susceptible to inactivation by avibactam. The R220A variant was purified and assessed via steady-state inhibition kinetics and found to possess increased K_i-app values and decreased k_inact/K_I or k₂/K values against all tested inhibitors compared to PenA1. Avibactam was the most affected by the alanine replacement at 220 with a nearly 400-fold decreased acylation rate. The X-ray crystal structure of the R220A variant was solved and revealed loss of the hydrogen bonding network between residues 237 and 276 leaving a void in the active site that was occupied instead by water molecules. Michaelis-Menten complexes were generated to elucidate the molecular contributions of the poorer in vitro inhibition profile of vaborbactam against PenA1 (k₂/K, 3.4 × 10² M^-1 s^-1) and was compared to KPC-2, a class A carbapenemase that is robustly inhibited by vaborbactam. The active site of PenA1 is larger than that of KPC-2, which impacted the ability of vaborbactam to form favorable interactions, and as a result the carboxylate of vaborbactam was drawn toward K234/T235 in PenA1 displacing the boronic acid from approaching the nucleophilic S70. Moreover, in PenA1, the tyrosine at position 105 compared to tryptophan in KPC-2, was more flexible rotating more than 90°, and as a result PenA1's Y105 competed for binding with the cyclic boronate vs the thiophene moiety of vaborbactam, further precluding inhibition of PenA1 by vaborbactam. Given the 400-fold decreased k₂/K for the R220A variant compared to PenA1, acyl-enzyme complexes were generated via molecular modeling and compared to the PenA1-avibactam crystal structure. The water molecules occupying the active site of the R220A variant are unable to stabilize the T237 and D276 region of the active site altering the ability of avibactam to form favorable interactions compared to PenA1. The former likely impacts the ability of all inhibitors to effectively acylate this variant enzyme. Based on the summation of all evidence herein, the utility of these newer β-lactamase inhibitors (i.e., relebactam, enmetazobactam, avibactam, and vaborbactam) in combination with a β-lactam against B. multivorans producing PenA1 and the R220A variant is promising.

Ab Initio Spectroscopic Investigation of Pharmacologically Relevant Chiral Molecules: The Cases of Avibactam, Cephems, and Idelalisib as Benchmarks for Antibiotics and Anticancer Drugs

The ability to accurately measure or predict several physicochemical properties of molecules which play a role as active substances in drugs can be of strategic importance for pharmacological applications, in addition to its possible interest in fundamental research. Chirality is a relevant feature in the characterization of drug molecules: enantiomers can show different pharmacological activity and adverse effects. The ability to separate stereoisomers and to assign their absolute configuration can thus be crucial. Circular dichroism (CD) spectra are a useful tool to distinguish between enantiomers. In this work we apply an in-house developed code, based on an efficient DFT approach for circular dichroism, to fully characterize the molecular optical properties in the case of few selected fundamental molecules for current medical and pharmaceutical research, namely avibactam, as representative of non β-lactam inhibitors, two cephems (cefepime and cefoxitin), as examples of β-lactam antibiotics, and idelalisib, as a recent relevant anticancer active substance to treat major leukemias. For the above molecules, in addition to their optical absorption spectra, we calculate their CD spectra within state-of-the-art computational techniques. We then investigate both the conformational and chemical sensitivity of absorption and CD spectra for the chosen molecules. The outcomes of the present research could be of fundamental importance to gain additional information on molecules involved in therapeutic protocols for severe diseases or in drug design.

Potent inhibitory activity of taniborbactam towards NDM-1 and NDM-1Q119X mutants, and in vitro activity of cefepime/taniborbactam against MBLs producing Enterobacterales

OBJECTIVE

This study aimed to investigate the in vitro activity of taniborbactam (VNRX-5133), a novel broad-spectrum bicyclic boronate, against NDM-1 and Q119E, Q119K, Q119C, Q119F, Q119V, and Q119Y NDM-1 variants, which showed an increased activity towards some β-lactams, including cefepime.

METHODS

Inhibition kinetic assays were spectrophotometrically performed using cefepime (50 μM) as the reporter substrate and 80 nM of each enzyme. Taniborbactam behaves as a competitive inhibitor towards NDM-1 and NDM-1 Q119 variants with lower Ki values (range 3-16 nM). The phenotypic profile was assessed in both Enterobacterales clinical isolates and engineered Escherichia coli BL21(DE3) strains by conventional broth microdilution procedures according to the Clinical and Laboratory Standards Institute (CLSI).

RESULTS

Taniborbactam at a fixed concentration of 4 mg/L was able to restore activity of cefepime in 24 of 26 Enterobacterales clinical isolates harbouring metallo-β-lactamases with MIC₅₀/MIC₉₀ values of 14 mg/L. Cefepime MICs were drastically reduced in all clinical isolates and in NDM-1 and Q119X producing Escherichia coli BL21(DE3). Taniborbactam was unable to restore susceptibility to cefepime in two IMP variants producing clinical isolates.

CONCLUSION

The inhibition level of NDM enzymes provided by taniborbactam protects the antibacterial activity of cefepime from this important metallo-β-lactamase.

In vitro Activity of Ceftazidime-Avibactam and Aztreonam-Avibactam Against Carbapenem-resistant Enterobacteriaceae Isolates Collected from Three Secondary Hospitals in Southwest China Between 2018 and 2019

Purpose

To assess the antimicrobial activities of ceftazidime/avibactam (CAZ/AVI) and aztreonam/avibactam (ATM/AVI) against carbapenem-resistant Enterobacteriaceae (CRE) isolates collected from three secondary hospitals in Southwest China between 2018 and 2019.

Materials and Methods

A total of 120 unique CRE clinical isolates were collected and carbapenemase genes were detected using PCR. Antimicrobial susceptibility was determined using standard broth microdilution method and the results were interpreted according to CLSI breakpoints.

Results

The 120 carbapenem-resistant strains included 92 Klebsiella pneumoniae, 10 Escherichia coli, 10 Enterobacter cloacae, five Klebsiella aerogenes, and three Klebsiella oxytoca isolates. Seventy-four percent of these 120 CRE isolates were collected from patients located in non-ICUs; 65.0% of these CRE isolates were collected from male patients; and 34.2% of these isolates were isolated from respiratory tracts. Four different carbapenemase genes were identified among 103 carbapenemase-producing Enterobacteriaceae (CPE) isolates, including bla _KPC-2 (n=77), bla _NDM-1 (n=16), bla _NDM-5 (n=12) and bla _IMP-4 (n=2). Overall, 21.7%, 37.5%, 40.8%, 75.0%, and 100% of the CRE strains were susceptible to levofloxacin, trimethoprim/sulfamethoxazole, amikacin, CAZ/AVI, and ATM/AVI, respectively. In addition, antimicrobial susceptibility testing showed that 96.7% isolates (n=116) were resistant to aztreonam, and the addition of avibactam (4 mg/L) significantly reduced the MICs of those aztreonam-resistant isolates by more than 128-fold (range: ≤0.125-4 mg/L), and 90.0% (n=108) of total 120 isolates were inhibited at ATM/AVI concentration ≤1 mg/L.

Conclusion

Our study revealed significant antimicrobial resistance among the CRE isolates against some commonly used antibiotics in three secondary Chinese hospitals. ATM/AVI exhibited potent activity against CRE isolates, including double carbapenemase-producing isolates, whereas CAZ/AVI was active against all KPC producers.

Activity of aztreonam in combination with ceftazidime-avibactam against serine- and metallo-β-lactamase-producing Pseudomonas aeruginosa

Existing data support the combination of aztreonam and ceftazidime-avibactam against serine-β-lactamase (SBL)- and metallo-β-lactamase (MBL)-producing Enterobacterales, although there is a paucity of data against SBL- and MBL-producing Pseudomonas aeruginosa. In this study, 5 SBL- and MBL-producing P. aeruginosa (1 IMP, 4 VIM) were evaluated against aztreonam and ceftazidime-avibactam alone and in combination via broth microdilution and time-kill analyses. All 5 isolates were nonsusceptible to aztreonam, aztreonam-avibactam, and ceftazidime-avibactam. Combining aztreonam with ceftazidime-avibactam at subinhibitory concentrations produced synergy and restored bactericidal activity in 4/5 (80%) isolates tested. These results suggest that the combination of aztreonam and ceftazidime-avibactam may be a viable treatment option against SBL- and MBL-producing P. aeruginosa.

Epidemiology and Diagnostics of Carbapenem Resistance in Gram-negative Bacteria

Carbapenem resistance in gram-negative bacteria has caused a global epidemic that continues to grow. Although carbapenemase-producing Enterobacteriaceae have received the most attention because resistance was first reported in these pathogens in the early 1990s, there is increased awareness of the impact of carbapenem-resistant nonfermenting gram-negative bacteria, such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia. Moreover, evaluating the problem of carbapenem resistance requires the consideration of both carbapenemase-producing bacteria as well as bacteria with other carbapenem resistance mechanisms. Advances in rapid diagnostic tests to improve the detection of carbapenem resistance and the use of large, population-based datasets to capture a greater proportion of carbapenem-resistant organisms can help us gain a better understanding of this urgent threat and enable physicians to select the most appropriate antibiotics.

Fluorogenic Probes/Inhibitors of β-Lactamase and their Applications in Drug-Resistant Bacteria

β-Lactam antibiotics are generally perceived as one of the greatest inventions of the 20^th century, and these small molecular compounds have saved millions of lives. However, upon clinical application of antibiotics, the β-lactamase secreted by pathogenic bacteria can lead to the gradual development of drug resistance. β-Lactamase is a hydrolase that can efficiently hydrolyze and destroy β-lactam antibiotics. It develops and spreads rapidly in pathogens, and the drug-resistant bacteria pose a severe threat to human health and development. As a result, detecting and inhibiting the activities of β-lactamase are of great value for the rational use of antibiotics and the treatment of infectious diseases. At present, many specific detection methods and inhibitors of β-lactamase have been developed and applied in clinical practice. In this Minireview, we describe the resistance mechanism of bacteria producing β-lactamase and further summarize the fluorogenic probes, inhibitors of β-lactamase, and their applications in the treatment of infectious diseases. It may be valuable to design fluorogenic probes with improved selectivity, sensitivity, and effectiveness to further identify the inhibitors for β-lactamases and eventually overcome bacterial resistance.

Bicyclic Boronates as Potent Inhibitors of AmpC, the Class C β-Lactamase from Escherichia coli

Resistance to β-lactam antibacterials, importantly via production of β-lactamases, threatens their widespread use. Bicyclic boronates show promise as clinically useful, dual-action inhibitors of both serine- (SBL) and metallo- (MBL) β-lactamases. In combination with cefepime, the bicyclic boronate taniborbactam is in phase 3 clinical trials for treatment of complicated urinary tract infections. We report kinetic and crystallographic studies on the inhibition of AmpC, the class C β‑lactamase from Escherichia coli, by bicyclic boronates, including taniborbactam, with different C-3 side chains. The combined studies reveal that an acylamino side chain is not essential for potent AmpC inhibition by active site binding bicyclic boronates. The tricyclic form of taniborbactam was observed bound to the surface of crystalline AmpC, but not at the active site, where the bicyclic form was observed. Structural comparisons reveal insights into why active site binding of a tricyclic form has been observed with the NDM-1 MBL, but not with other studied β-lactamases. Together with reported studies on the structural basis of inhibition of class A, B and D β‑lactamases, our data support the proposal that bicyclic boronates are broad-spectrum β‑lactamase inhibitors that work by mimicking a high energy 'tetrahedral' intermediate. These results suggest further SAR guided development could improve the breadth of clinically useful β-lactamase inhibition.

Broad Spectrum β-Lactamase Inhibition by a Thioether Substituted Bicyclic Boronate

β-Lactamases comprise the most widely used mode of resistance to β-lactam antibiotics. Cyclic boronates have shown promise as a new class of β-lactamase inhibitor, with pioneering potential to potently inhibit both metallo- and serine-β-lactamases. We report studies concerning a bicyclic boronate ester with a thioether rather than the more typical β-lactam antibiotic "C-6/C-7" acylamino type side chain, which is present in the penicillin/cephalosporin antibiotics. The thioether bicyclic boronate ester was tested for activity against representative serine- and metallo-β-lactamases. The results support the broad inhibition potential of bicyclic boronate based inhibitors with different side chains, including against metallo-β-lactamases from B1, B2, and B3 subclasses. Combined with previous crystallographic studies, analysis of a crystal structure of the thioether inhibitor with the clinically relevant VIM-2 metallo-β-lactamase implies that further SAR work will expand the already broad scope of β-lactamase inhibition by bicyclic boronates.

Development of a selective media for detecting Campylobacter spp. in chicken carcasses using avibactam supplemented mCCDA

Campylobacter spp. are major causes of gastrointestinal infections worldwide, and are commonly identified using modified-charcoal-cefoperazone-deoxycholate agar (mCCDA). However, the efficacy of this screening technique is often hindered by overgrowth of competing flora, such as extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Thus, in the present study we supplemented mCCDA with a recently developed ESBL inhibitor, avibactam (A-mCCDA). We inoculated mCCDA and A-mCCDA plates with 25 strains each of Campylobacter spp. and ESBL-producing E. coli, and thereby determined that the optimum avibactam concentration required to inhibit ESBL-producing E. coli was 0.0625 mg/L. At this concentration, a significantly higher proportion of Campylobacter spp. was isolated using A-mCCDA compared to that using mCCDA (P < 0.05). Thus, the results of the present study support the use of A-mCCDA to improve current Campylobacter screening methods.

Cyclic boronates as versatile scaffolds for KPC-2 β-lactamase inhibition

Klebsiella pneumoniae carbapenemase-2 (KPC-2) is a serine-β-lactamase (SBL) capable of hydrolysing almost all β-lactam antibiotics. We compare KPC-2 inhibition by vaborbactam, a clinically-approved monocyclic boronate, and VNRX-5133 (taniborbactam), a bicyclic boronate in late-stage clinical development. Vaborbactam inhibition is slowly reversible, whereas taniborbactam has an off-rate indicating essentially irreversible complex formation and a 15-fold higher on-rate, although both potentiate β-lactam activity against KPC-2-expressing K. pneumoniae. High resolution X-ray crystal structures reveal closely related binding modes for both inhibitors to KPC-2, with differences apparent only in positioning of the endocyclic boronate ester oxygen. The results indicate the bicyclic boronate scaffold as both an efficient, long-lasting, KPC-2 inhibitor and capable of supporting further iterations that may improve potency against specific enzyme targets and pre-empt the emergence of inhibitor resistant KPC-2 variants.

Monitoring protein-metal binding by 19F NMR - a case study with the New Delhi metallo-β-lactamase 1

19F NMR protein observed spectroscopy is evaluated as a method for analysing protein metal binding using the New Delhi metallo-β-lactamase 1. The results imply 19F NMR is useful for analysis of different metallated protein states and investigations on equilibrium states in the presence of inhibitors. One limitation is that 19F labelling may affect metal ion binding. The sensitive readout of changes in protein behaviour observed by 19F NMR spectra coupled with the broad scope of tolerated conditions (e.g. buffer variations) means 19F NMR should be further investigated for studying metal ion interactions and the inhibition of metallo-enzymes during drug discovery.

In vitro efficacy of imipenem-relebactam and cefepime-AAI101 against a global collection of ESBL-positive and carbapenemase-producing Enterobacteriaceae

OBJECTIVES

To evaluate the potential clinical in vitro efficacy of novel β-lactam/β-lactamase-inhibitor combinations - including imipenem-relebactam (IPM-REL) and cefepime-AAI101 (enmetazobactam) (FEP-AAI) - against contemporary multidrug-resistant (MDR) Enterobacteriaceae.

METHODS

Agar-based MIC screening against MDR Enterobacteriaceae (n = 264) was used to evaluate the in vitro efficacy of IPM-REL and FEP-AAI, to compare the results with established combinations, and to investigate alternative β-lactam partners for relebactam (REL) and enmetazobactam (AAI). The inhibition activities of REL, AAI and the comparators avibactam (AVI) and tazobactam, against isolated recombinant β-lactamases covering representatives from all four Ambler classes of β-lactamases, were tested using a fluorescence-based assay.

RESULTS

Using recombinant proteins, all four inhibitors were highly active against the tested class A serine β-lactamases (SBLs). REL and AVI showed moderate activity against the Class C AmpC from Pseudomonas aeruginosa and the Class D OXA-10/-48 SBLs, but outperformed tazobactam and AAI. All tested inhibitors lacked activity against Class B metallo-β-lactamases (MBLs). In the presence of REL and IPM, but not AAI, susceptibility increased against Klebsiella pnuemoniae carbapenemase (KPC)-positive and OXA-48-positive isolates. Both aztreonam-AVI and ceftolozane-tazobactam were more effective than IPM-REL. In all the tested combinations, AAI was a more effective inhibitor of class A β-lactamases (ESBLs) than the established inhibitors.

CONCLUSION

The results lead to the proposal of alternative combination therapies involving REL and AAI to potentiate the use of β-lactams against clinical Gram-negative isolates expressing a variety of lactamases. They highlight the potential of novel combinations for combating strains not covered by existing therapies.

Synthetic approaches towards avibactam and other diazabicyclooctane β-lactamase inhibitors

The synthetic strategies to obtain avibactam and other diazabicyclooctane β-lactamase inhibitors such as ETX2514 are presented.

Synthesis and antibacterial evaluation against resistant Gram-negative bacteria of monobactams bearing various substituents on oxime residue

Based on the structural characteristics of aztreonam (AZN) and its target PBP3, a series of new monobactam derivatives bearing various substituents on oxime residue were prepared and evaluated for their antibacterial activities against susceptible and resistant Gram-negative bacteria. Among them, compounds 8p and 8r displayed moderate potency with MIC values of 0.125-32 μg/mL against most tested Gram-negative strains, comparable to AZN. Meanwhile, the combination of 8p and 8r with avibactam as a β-lactamases inhibitor, in a ratio of 1:16, showed a promising synergistic effect against both ESBLs- and NDM-1-producing K. pneumoniae, with significantly reduced MIC values up to 8-fold and >256-fold respectively. Furthermore, both of them demonstrated excellent safety profiles both in vitro and in vivo. The results provided powerful information for further structural optimization of monobactam antibiotics to fight β-lactamase-producing resistant Gram-negative bacteria.

Epidemiology and Treatment of Multidrug-Resistant and Extensively Drug-Resistant Pseudomonas aeruginosa Infections

In recent years, the worldwide spread of the so-called high-risk clones of multidrug-resistant or extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa has become a public health threat. This article reviews their mechanisms of resistance, epidemiology, and clinical impact and current and upcoming therapeutic options. In vitro and in vivo treatment studies and pharmacokinetic and pharmacodynamic (PK/PD) models are discussed. Polymyxins are reviewed as an important therapeutic option, outlining dosage, pharmacokinetics and pharmacodynamics, and their clinical efficacy against MDR/XDR P. aeruginosa infections. Their narrow therapeutic window and potential for combination therapy are also discussed. Other "old" antimicrobials, such as certain β-lactams, aminoglycosides, and fosfomycin, are reviewed here. New antipseudomonals, as well as those in the pipeline, are also reviewed. Ceftolozane-tazobactam has clinical activity against a significant percentage of MDR/XDR P. aeruginosa strains, and its microbiological and clinical data, as well as recommendations for improving its use against these bacteria, are described, as are those for ceftazidime-avibactam, which has better activity against MDR/XDR P. aeruginosa, especially strains with certain specific mechanisms of resistance. A section is devoted to reviewing upcoming active drugs such as imipenem-relebactam, cefepime-zidebactam, cefiderocol, and murepavadin. Finally, other therapeutic strategies, such as use of vaccines, antibodies, bacteriocins, anti-quorum sensing, and bacteriophages, are described as future options.

Bicyclic Boronate VNRX-5133 Inhibits Metallo- and Serine-β-Lactamases

The bicyclic boronate VNRX-5133 (taniborbactam) is a new type of β-lactamase inhibitor in clinical development. We report that VNRX-5133 inhibits serine-β-lactamases (SBLs) and some clinically important metallo-β-lactamases (MBLs), including NDM-1 and VIM-1/2. VNRX-5133 activity against IMP-1 and tested B2/B3 MBLs was lower/not observed. Crystallography reveals how VNRX-5133 binds to the class D SBL OXA-10 and MBL NDM-1. The crystallographic results highlight the ability of bicyclic boronates to inhibit SBLs and MBLs via binding of a tetrahedral (sp³) boron species. The structures imply conserved binding of the bicyclic core with SBLs/MBLs. With NDM-1, by crystallography, we observed an unanticipated VNRX-5133 binding mode involving cyclization of its acylamino oxygen onto the boron of the bicyclic core. Different side-chain binding modes for bicyclic boronates for SBLs and MBLs imply scope for side-chain optimization. The results further support the “high-energy-intermediate” analogue approach for broad-spectrum β-lactamase inhibitor development and highlight the ability of boron inhibitors to interchange between different hybridization states/binding modes.

Heteroaryl Phosphonates as Noncovalent Inhibitors of Both Serine- and Metallocarbapenemases

Gram-negative pathogens expressing serine β-lactamases (SBLs) and metallo-β-lactamases (MBLs), especially those with carbapenemase activity, threaten the clinical utility of almost all β-lactam antibiotics. Here we describe the discovery of a heteroaryl phosphonate scaffold that exhibits noncovalent cross-class inhibition of representative carbapenemases, specifically the SBL KPC-2 and the MBLs NDM-1 and VIM-2. The most potent lead, compound 16, exhibited low nM to low μM inhibition of KPC-2, NDM-1, and VIM-2. Compound 16 potentiated imipenem efficacy against resistant clinical and laboratory bacterial strains expressing carbapenemases while showing some cytotoxicity toward human HEK293T cells only at concentrations above 100 μg/mL. Complex structures with KPC-2, NDM-1, and VIM-2 demonstrate how these inhibitors achieve high binding affinity to both enzyme classes. These findings provide a structurally and mechanistically new scaffold for drug discovery targeting multidrug resistant Gram-negative pathogens and more generally highlight the active site features of carbapenemases that can be leveraged for lead discovery.

Non-inferiority versus superiority trial design for new antibiotics in an era of high antimicrobial resistance: the case for post-marketing, adaptive randomised controlled trials

Antimicrobial resistance is one of the most important threats to global health security. A range of Gram-negative bacteria associated with high morbidity and mortality are now resistant to almost all available antibiotics. In this context of urgency to develop novel drugs, new antibiotics for multidrug-resistant Gram-negative bacteria (namely, ceftazidime-avibactam, plazomicin, and meropenem-vaborbactam) have been approved by regulatory authorities based on non-inferiority trials that provided no direct evidence of their efficacy against multidrug-resistant bacteria such as Enterobacteriaceae spp, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Burkholderia cepacia, and Acinetobacter baumannii. The use of non-inferiority and superiority trials, and selection of appropriate and optimal study designs, remains a major challenge in the development, registration, and post-marketing implementation of new antibiotics. Using an example of the development process of ceftazidime-avibactam, we propose a strategy for a new research framework based on adaptive randomised clinical trials. The operational research strategy has the aim of assessing the efficacy of new antibiotics in special groups of patients, such as those infected with multidrug-resistant bacteria, who were not included in earlier phase studies, and for whom it is important to establish an appropriate standard of care.