New promising β-lactamase inhibitors for clinical use

Interplay between the β-lactam side chain and an active-site mobile loop of NDM-1 in penicillin hydrolysis as a potential target for mechanism-based inhibitor design

Metallo-β-lactamases (MβLs) stand as significant resistant mechanism against β-lactam antibiotics in Gram-negative bacteria. The worldwide dissemination of New Delhi metallo-β-lactamases (NDMs) intensifies antimicrobial resistance, posing severe threats to human health due to the absence of inhibitors available in clinical therapy. L3, a flexible β-hairpin loop flanking the active site in MβLs, has been proven to wield influence over the reaction process by assuming a crucial role in substrate recognition and intermediate stabilization. In principle, it potentially retards product release from the enzyme, consequently reducing the overall turnover rate although the details regarding this aspect remain inadequately elucidated. In this study, we crystallized NDM-1 in complex with three penicillin substrates, conducted molecular dynamics simulations, and measured the steady-state kinetic parameters. These analyses consistently unveiled substantial disparities in their interactions with loop L3. We further synthesized a penicillin V derivative with increased hydrophobicity in the R1 side chain and co-crystallized it with NDM-1. Remarkably, this compound exhibited much stronger dynamic interplay with L3 during molecular dynamics simulation, showed much lower Km and kcat values, and demonstrated moderate inhibitory capacity to NDM-1 catalyzed meropenem hydrolysis. The data presented here may provide a strategic approach for designing mechanism-based MβL inhibitors focusing on structural elements external to the enzyme's active center.

Novel Beta Lactam Antibiotics for the Treatment of Multidrug-Resistant Gram-Negative Infections in Children: A Narrative Review

Infections due to carbapenem-resistant Enterobacterales (CRE) are increasingly prevalent in children and are associated with poor clinical outcomes, especially in critically ill patients. Novel beta lactam antibiotics, including ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-cilastatin-relebactam, and cefiderocol, have been released in recent years to face the emerging challenge of multidrug-resistant (MDR) Gram-negative bacteria. Nonetheless, several novel agents lack pediatric indications approved by the Food and Drug Administration (FDA) and the European Medicine Agency (EMA), leading to uncertain pediatric-specific treatment strategies and uncertain dosing regimens in the pediatric population. In this narrative review we have summarized the available clinical and pharmacological data, current limitations and future prospects of novel beta lactam antibiotics in the pediatric population.

Extended and Continuous Infusion of Novel Protected β-Lactam Antibiotics: A Narrative Review

Consolidated data from pharmacokinetic and pharmacodynamic studies support the administration of β-lactam antibiotics in prolonged infusion (i.e., extended or continuous) to optimize therapeutic efficacy by increasing the probability of attaining maximal bactericidal activity. This is the longest possible time during which the free drug concentrations are approximately four-fold the minimum inhibitory concentration between dosing intervals. In the context of antimicrobial stewardship strategies, achieving aggressive pharmacokinetic and pharmacodynamic targets is an important tool in the management of multi-drug resistant (MDR) bacterial infections and in the attainment of mutant preventing concentrations. However, prolonged infusion remains an unexploited resource. Novel β-lactam/β-lactamase inhibitor (βL/βLI) combinations (ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-cilastatin-relebactam) have been released in recent years to face the emerging challenge of MDR Gram-negative bacteria. Pre-clinical and real-life evidence has confirmed the promising role of prolonged infusion of these molecules in specific settings and clinical populations. In this narrative review we have summarized available pharmacological and clinical data, future perspectives, and current limitations of prolonged infusion of the novel protected β-lactams, their application in hospital settings and in the context of outpatient parenteral antimicrobial therapy.

Deciphering the antimicrobial, antibiofilm and membrane stabilizing synergism of Mikania scandens (L.) Willd. leaves and stems substantiation through in vitro and in silico studies

Considering the traditional application of Mikania scandens (L.) Willd. against wounds and itching. Leaves (MSL) and stems (MSS) were sequentially extracted using solvents petroleum-ether, carbon-tetrachloride, chloroform, ethyl-acetate and ethanol. Disk-diffusion assay revealed the ethyl acetate MSL and MSS extracts were the prominent against ten bacteria, five carbapenem-resistant bacteria and one fungal strains. Subsequent quantitative antimicrobial analysis specified MSL extractives more potent over MSS with lower 1500 and 3500µg/ml MIC and MBC value in both gram-negative and positive bacteria. These sturdiest ethyl-acetate MSL extractives antimicrobial efficiency also fostered fungicidal activity having lower 100µg/ml MFC. Whereat, almost homologous 160-180 min timing noted liken to standard ciprofloxacin susceptibility in both strains, 75% biofilm inhibition at 2×MIC concentration along with 92±0.2% membrane stabilizing activities over synthetic counterparts prospected in preceding standard extractives. Computational molecular docking of MSL compounds supported this findings therefore forego this valuable synergistic insight as antimicrobial agents to efficiently eradicate human infections.

Metal binding pharmacophore click-derived discovery of new broad-spectrum metallo-β-lactamase inhibitors

The emergence of metallo-β-lactamases (MBLs) confers resistance to nearly all the β-lactam antibiotics, including carbapenems. Currently, there is a lack of clinically useful MBL inhibitors, making it crucial to discover new inhibitor chemotypes that can potently target multiple clinically relevant MBLs. Herein we report a strategy that utilizes a metal binding pharmacophore (MBP) click approach to identify new broad-spectrum MBL inhibitors. Our initial investigation identified several MBPs including phthalic acid, phenylboronic acid and benzyl phosphoric acid, which were subjected to structural transformations using azide-alkyne click reactions. Subsequent structure-activity relationship analyses led to the identification of several potent broad-spectrum MBL inhibitors, including 73 that manifested IC₅₀ values ranging from 0.00012 μM to 0.64 μM against multiple MBLs. Co-crystallographic studies demonstrated the importance of MBPs in engaging with the MBL active site anchor pharmacophore features, and revealed the unusual two-molecule binding modes with IMP-1, highlighting the critical role of flexible active site loops in recognizing structurally diverse substrates/inhibitors. Our work provides new chemotypes for MBL inhibition and establishes a MBP click-derived paradigm for inhibitor discovery targeting MBLs as well as other metalloenzymes.

PHT427 as an effective New Delhi metallo-β-lactamase-1 (NDM-1) inhibitor restored the susceptibility of meropenem against Enterobacteriaceae producing NDM-1

Introduction

With the increasingly serious problem of bacterial drug resistance caused by NDM-1, it is an important strategy to find effective inhibitors to assist β-lactam antibiotic treatment against NDM-1 resistant bacteria. In this study, PHT427 (4-dodecyl-N-1,3,4-thiadiazol-2-yl-benzenesulfonamide) was identified as a novel NDM-1 inhibitor and restored the susceptibility of meropenem against Enterobacteriaceae producing NDM-1.

Methods

We used a high throughput screening model to find NDM-1 inhibitor in the library of small molecular compounds. The interaction between the hit compound PHT427 and NDM-1 was analyzed by fluorescence quenching, surface plasmon resonance (SPR) assay, and molecular docking analysis. The efficacy of the compound in combination with meropenem was evaluated by determining the FICIs of Escherichia coli BL21(DE3)/pET30a(+)-bla _NDM-1 and Klebsiella pneumoniae clinical strain C1928 (producing NDM-1). In addition, the mechanism of the inhibitory effect of PHT427 on NDM-1 was studied by site mutation, SPR, and zinc supplementation assays.

Results

PHT427 was identified as an inhibitor of NDM-1. It could significantly inhibit the activity of NDM-1 with an IC₅₀ of 1.42 μmol/L, and restored the susceptibility of meropenem against E. coli BL21(DE3)/pET30a(+)-bla _NDM-1 and K. pneumoniae clinical strain C1928 (producing NDM-1) in vitro. The mechanism study indicated that PHT427 could act on the zinc ions at the active site of NDM-1 and the catalytic key amino acid residues simultaneously. The mutation of Asn220 and Gln123 abolished the affinity of NDM-1 by PHT427 via SPR assay.

Discussion

This is the first report that PHT427 is a promising lead compound against carbapenem-resistant bacteria and it merits chemical optimization for drug development.

Resistance to Ceftazidime/Avibactam, Meropenem/Vaborbactam and Imipenem/Relebactam in Gram-Negative MDR Bacilli: Molecular Mechanisms and Susceptibility Testing

Multidrug resistance (MDR) represents a serious global threat due to the rapid global spread and limited antimicrobial options for treatment of difficult-to-treat (DTR) infections sustained by MDR pathogens. Recently, novel β-lactams/β-lactamase inhibitor combinations (βL-βLICs) have been developed for the treatment of DTR infections due to MDR Gram-negative pathogens. Although novel βL-βLICs exhibited promising in vitro and in vivo activities against MDR pathogens, emerging resistances to these novel molecules have recently been reported. Resistance to novel βL-βLICs is due to several mechanisms including porin deficiencies, increasing carbapenemase expression and/or enzyme mutations. In this review, we summarized the main mechanisms related to the resistance to ceftazidime/avibactam, meropenem/vaborbactam and imipenem/relebactam in MDR Gram-negative micro-organisms. We focused on antimicrobial activities and resistance traits with particular regard to molecular mechanisms related to resistance to novel βL-βLICs. Lastly, we described and discussed the main detection methods for antimicrobial susceptibility testing of such molecules. With increasing reports of resistance to novel βL-βLICs, continuous attention should be maintained on the monitoring of the phenotypic traits of MDR pathogens, into the characterization of related mechanisms, and on the emergence of cross-resistance to these novel antimicrobials.

β-Lactam Antibiotics and β-Lactamase Enzymes Inhibitors, Part 2: Our Limited Resources

β-lactam antibiotics (BLAs) are crucial molecules among antibacterial drugs, but the increasing emergence of resistance to them, developed by bacteria producing β-lactamase enzymes (BLEs), is becoming one of the major warnings to the global public health. Since only a small number of novel antibiotics are in development, a current clinical approach to limit this phenomenon consists of administering proper combinations of β-lactam antibiotics (BLAs) and β-lactamase inhibitors (BLEsIs). Unfortunately, while few clinically approved BLEsIs are capable of inhibiting most class-A and -C serine β-lactamases (SBLEs) and some carbapenemases of class D, they are unable to inhibit most part of the carbapenem hydrolyzing enzymes of class D and the worrying metallo-β-lactamases (MBLEs) of class B. Particularly, MBLEs are a set of enzymes that catalyzes the hydrolysis of a broad range of BLAs by a zinc-mediated mechanism, and currently no clinically available molecule capable of inhibiting MBLEs exists. Additionally, new types of alarming “superbugs”, were found to produce the New Delhi metallo-β-lactamases (NDMs) encoded by increasing variants of a plasmid-mediated gene capable of rapidly spreading among bacteria of the same species and even among different species. Particularly, NDM-1 possesses a flexible hydrolysis mechanism that inactivates all BLAs, except for aztreonam. The present review provides first an overview of existing BLAs and the most clinically relevant BLEs detected so far. Then, the BLEsIs and their most common associations with BLAs already clinically applied and those still in development are reviewed.

Recommendations to Synthetize Old and New β-Lactamases Inhibitors: A Review to Encourage Further Production

The increasing emergence of bacteria producing β-lactamases enzymes (BLEs), able to inactivate the available β-lactam antibiotics (BLAs), causing the hydrolytic opening of their β-lactam ring, is one of the global major warnings. According to Ambler classification, BLEs are grouped in serine-BLEs (SBLEs) of class A, C, and D, and metal-BLEs (MBLEs) of class B. A current strategy to restore no longer functioning BLAs consists of associating them to β-lactamase enzymes inhibitors (BLEsIs), which, interacting with BLEs, prevent them hydrolyzing to the associated antibiotic. Worryingly, the inhibitors that are clinically approved are very few and inhibit only most of class A and C SBLEs, leaving several class D and all MBLEs of class B untouched. Numerous non-clinically approved new molecules are in development, which have shown broad and ultra-broad spectrum of action, some of them also being active on the New Delhi metal-β-lactamase-1 (NDM-1), which can hydrolyze all available BLAs except for aztreonam. To not duplicate the existing review concerning this topic, we have herein examined BLEsIs by a chemistry approach. To this end, we have reviewed both the long-established synthesis adopted to prepare the old BLEsIs, those proposed to achieve the BLEsIs that are newly approved, and those recently reported to prepare the most relevant molecules yet in development, which have shown high potency, providing for each synthesis the related reaction scheme.

New Antibiotics for Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) represent one of the most common hospital-acquired infections, carrying a significant morbidity and risk of mortality. Increasing antibiotic resistance among the common bacterial pathogens associated with HAP and VAP, especially Enterobacterales and nonfermenting gram-negative bacteria, has made the choice of empiric treatment of these infections increasingly challenging. Moreover, failure of initial empiric therapy to cover the causative agents associated with HAP and VAP has been associated with worse clinical outcomes. This review provides an overview of antibiotics newly approved or in development for the treatment of HAP and VAP. The approved antibiotics include ceftobiprole, ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, and cefiderocol. Their major advantages include their high activity against multidrug-resistant gram-negative pathogens.

Susceptibility to Imipenem/Relebactam of Pseudomonas aeruginosa and Acinetobacter baumannii Isolates from Chinese Intra-Abdominal, Respiratory and Urinary Tract Infections: SMART 2015 to 2018

Purpose

In recent years, less options are available for treating carbapenem-resistant Acinetobacter baumannii and carbapenem-resistant Pseudomonas aeruginosa. The present study investigates the susceptibility rates to imipenem/relebactam for the treatment of intra-abdominal infections (IAIs), respiratory tract infections (RTIs) and urinary tract infections (UTIs) caused by A. baumannii and P. aeruginosa in China.

Patients and Methods

A total of 1886 P. aeruginosa and 1889 A. baumannii isolates were collected in 21 centers (7 regions) as a part of the global SMART surveillance program between 2015 and 2018. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) recommendations using the broth microdilution methodology at Peking Union Medical College Hospital.

Results

For P. aeruginosa, overall susceptibility rates to imipenem/relebactam were 84.2% at a CLSI breakpoint of ≤2 mg/L compared to 55.7% for imipenem. Susceptibility rates of imipenem-non-susceptible P. aeruginosa to imipenem/relebactam were 64.4% and for multidrug-resistance (MDR) P. aeruginosa susceptibility rates were increased from 25.2% for imipenem to 65.8% for imipenem/relebactam. The susceptibilities of imipenem-non-susceptible and MDR P. aeruginosa strains were similarly restored by imipenem/relebactam in non-ICU and ICU wards. The rate of imipenem-non-susceptibilities A. baumannii isolates was 79.0%, whereas the MDR rate was 81.9%. Relebactam did not change the susceptibilities of imipenem-non susceptible or MDR A. baumannii isolates.

Conclusion

Imipenem/relebactam provides a therapy option to treat infections caused by MDR or imipenem-non-susceptible P. aeruginosa but not A. baumannii infections in China.

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.

Mechanistic Insight into Antimicrobial and Antioxidant Potential of Jasminum Species: A Herbal Approach for Disease Management

Drug resistance among microbial pathogens and oxidative stress caused by reactive oxygen species are two of the most challenging global issues. Firstly, drug-resistant pathogens cause several fatalities every year. Secondly aging and a variety of diseases, such as cardiovascular disease and cancer, are associated with free radical generated oxidative stress. The treatments currently available are limited, ineffective, or less efficient, so there is an immediate need to tackle these issues by looking for new therapies to resolve resistance and neutralize the harmful effects of free radicals. In the 21st century, the best way to save humans from them could be by using plants as well as their bioactive constituents. In this specific context, Jasminum is a major plant genus that is used in the Ayurvedic system of medicine to treat a variety of ailments. The information in this review was gathered from a variety of sources, including books, websites, and databases such as Science Direct, PubMed, and Google Scholar. In this review, a total of 14 species of Jasminum have been found to be efficient and effective against a wide variety of microbial pathogens. In addition, 14 species were found to be active free radical scavengers. The review is also focused on the disorders related to oxidative stress, and it was concluded that Jasminum grandiflorum and J. sambac normalized various parameters that were elevated by free radical generation. Alkaloids, flavonoids (rutoside), terpenes, phenols, and iridoid glucosides are among the main phytoconstituents found in various Jasminum species. Furthermore, this review also provides insight into the mechanistic basis of drug resistance, the generation of free radicals, and the role of Jasminum plants in combating resistance and neutralizing free radicals.

6-Halopyridylmethylidene Penicillin-Based Sulfones Efficiently Inactivate the Natural Resistance of Pseudomonas aeruginosa to β-Lactam Antibiotics

Pseudomonas aeruginosa, a major cause of nosocomial infections, is considered a paradigm of antimicrobial resistance, largely due to hyperproduction of chromosomal cephalosporinase AmpC. Here, we explore the ability of 6-pyridylmethylidene penicillin-based sulfones 1-3 to inactivate the AmpC β-lactamase and thus rescue the activity of the antipseudomonal ceftazidime. These compounds increased the susceptibility to ceftazidime in a collection of clinical isolates and PAO1 mutant strains with different ampC expression levels and also improved the inhibition kinetics relative to avibactam, displaying a slow deacylation rate and involving the formation of an indolizine adduct. Bromide 2 was the inhibitor with the lowest K_I (15.6 nM) and the highest inhibitory efficiency (k_inact/K_I). Computational studies using diverse AmpC enzymes revealed that the aromatic moiety in 1-3 targets a tunnel-like site adjacent to the catalytic serine and induces the folding of the H10 helix, indicating the potential value of this not-always-evident pocket in drug design.

In Vitro Activity of Imipenem/Relebactam Against Enterobacteriaceae Isolates Obtained from Intra-abdominal, Respiratory Tract, and Urinary Tract Infections in China: Study for Monitoring Antimicrobial Resistance Trends (SMART), 2015-2018

BACKGROUND

Considering the increasing incidence of carbapenem-resistant Enterobacteriaceae in China, this study aimed to establish the in vitro effectiveness of imipenem/relebactam (IMI/REL) on clinical Enterobacteriaceae isolates derived from intra-abdominal infections (IAIs), respiratory tract infections (RTIs), and urinary tract infections (UTIs) in China between 2015 and 2018.

METHODS

In total, 8781 Enterobacteriaceae isolates from IAI, RTI, and UTI samples were collected from 22 hospitals across 7 geographic regions of China. Susceptibility to antimicrobial drugs was tested using the Clinical and Laboratory Standards Institute broth microdilution and breakpoints, and IMI/REL activity was assessed using United States Food and Drug Administration guidelines.

RESULTS

In 2015-2018, the most frequently identified Enterobacteriaceae species was Escherichia coli (n = 4676 [53.3%]), followed by Klebsiella pneumoniae (n = 2949 [33.6%]) and Enterobacter cloacae (n = 542 [6.2%]). The Enterobacteriaceae isolates showed 95.2% overall susceptibility to IMI/REL, of which the susceptibility rates in isolates from IAI, RTI, and UTI were 95.8%, 91.4%, and 96.6%, respectively. Overall, the susceptibilities of both intensive care unit (ICU) and non-ICU Enterobacteriaceae isolates to colistin were 92.9%, followed by IMI/REL (90.7% [95.9%]) and amikacin (83.3% [92.3%]). In addition, IMI/REL restored 66.3% susceptibility in imipenem-nonsusceptible Enterobacteriaceae.

CONCLUSIONS

Given their high in vitro susceptibility, Enterobacteriaceae infections in China should be considered for IMI/REL treatment, especially with isolates that are not susceptible to carbapenems.

Imipenem/cilastatin/relebactam: A new carbapenem β-lactamase inhibitor combination

PURPOSE

The pharmacology, pharmacokinetics, pharmacodynamics, antimicrobial activity, efficacy, safety, and current regulatory status of imipenem/cilastatin/relebactam are reviewed.

SUMMARY

Imipenem/cilastatin/relebactam is a newly approved anti-infective combination of a well-established β-lactam and a new β-lactamase inhibitor for the treatment of complicated urinary tract infections (cUTIs), including pyelonephritis, and complicated intra-abdominal infections (cIAIs) caused by susceptible gram-negative bacteria in patients 18 years of age or older with limited or no alternative treatment options. The antibiotic is also indicated for the treatment of hospital-acquired bacterial pneumonia (HABP) and ventilator-associated bacterial pneumonia (VABP). The antibiotic is active in vitro against a wide range of pathogens, including multidrug-resistant (MDR) Pseudomonas aeruginosa and carbapenem-resistant Enterobacterales (CRE) such as Klebsiella pneumoniae carbapenemase. The addition of relebactam does not restore the activity of imipenem against metallo-β-lactamase (MBL)-producing Enterobacterales and carbapenem-resistant Acinetobacter baumannii. Two phase 3 clinical trials of imipenem/cilastatin/relebactam were conducted. In the RESTORE-IMI 1 trial, the efficacy and safety of imipenem/cilastatin/relebactam was found to be comparable to that of imipenem/cilastatin plus colistin for the treatment of infections caused by imipenem-nonsusceptible gram-negative bacteria in patients with HABP/VABP, cUTIs, and cIAIs, with a significantly lower incidence of nephrotoxicity reported with the new antibiotic. The RESTORE-IMI 2 trial demonstrated the noninferiority of imipenem/cilastatin/relebactam to piperacillin/tazobactam for the treatment of HABP/VABP. Commonly reported adverse events in clinical trials included anemia, elevated liver enzymes, electrolyte imbalances, nausea, vomiting, diarrhea, headache, fever, phlebitis and/or infusion-site reactions, and hypertension.

CONCLUSION

Imipenem/cilastatin/relebactam is a new β-lactam/β-lactamase inhibitor combination with activity against MDR gram-negative bacteria, including many CRE but excluding MBL-producing Enterobacterales and carbapenem-resistant Acinetobacter baumannii. It is approved for the treatment of cUTIs, cIAIs, and HABP/VABP.

New β-Lactam-β-Lactamase Inhibitor Combinations

The limited armamentarium against drug-resistant Gram-negative bacilli has led to the development of several novel β-lactam-β-lactamase inhibitor combinations (BLBLIs). In this review, we summarize their spectrum of in vitro activities, mechanisms of resistance, and pharmacokinetic-pharmacodynamic (PK-PD) characteristics. A summary of available clinical data is provided per drug. Four approved BLBLIs are discussed in detail. All are options for treating multidrug-resistant (MDR) Enterobacterales and Pseudomonas aeruginosa Ceftazidime-avibactam is a potential drug for treating Enterobacterales producing extended-spectrum β-lactamase (ESBL), Klebsiella pneumoniae carbapenemase (KPC), AmpC, and some class D β-lactamases (OXA-48) in addition to carbapenem-resistant Pseudomonas aeruginosa Ceftolozane-tazobactam is a treatment option mainly for carbapenem-resistant P. aeruginosa (non-carbapenemase producing), with some activity against ESBL-producing Enterobacterales Meropenem-vaborbactam has emerged as treatment option for Enterobacterales producing ESBL, KPC, or AmpC, with similar activity as meropenem against P. aeruginosa Imipenem-relebactam has documented activity against Enterobacterales producing ESBL, KPC, and AmpC, with the combination having some additional activity against P. aeruginosa relative to imipenem. None of these drugs present in vitro activity against Enterobacterales or P. aeruginosa producing metallo-β-lactamase (MBL) or against carbapenemase-producing Acinetobacter baumannii Clinical data regarding the use of these drugs to treat MDR bacteria are limited and rely mostly on nonrandomized studies. An overview on eight BLBLIs in development is also provided. These drugs provide various levels of in vitro coverage of carbapenem-resistant Enterobacterales, with several drugs presenting in vitro activity against MBLs (cefepime-zidebactam, aztreonam-avibactam, meropenem-nacubactam, and cefepime-taniborbactam). Among these drugs, some also present in vitro activity against carbapenem-resistant P. aeruginosa (cefepime-zidebactam and cefepime-taniborbactam) and A. baumannii (cefepime-zidebactam and sulbactam-durlobactam).

New Carbapenemase Inhibitors: Clearing the Way for the β-Lactams

Carbapenem resistance is a major global health problem that seriously compromises the treatment of infections caused by nosocomial pathogens. Resistance to carbapenems mainly occurs via the production of carbapenemases, such as VIM, IMP, NDM, KPC and OXA, among others. Preclinical and clinical trials are currently underway to test a new generation of promising inhibitors, together with the recently approved avibactam, relebactam and vaborbactam. This review summarizes the main, most promising carbapenemase inhibitors synthesized to date, as well as their spectrum of activity and current stage of development. We particularly focus on β-lactam/β-lactamase inhibitor combinations that could potentially be used to treat infections caused by carbapenemase-producer pathogens of critical priority. The emergence of these new combinations represents a step forward in the fight against antimicrobial resistance, especially in regard to metallo-β-lactamases and carbapenem-hydrolysing class D β-lactamases, not currently inhibited by any clinically approved inhibitor.

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.

Virtual screening identifies broad-spectrum β-lactamase inhibitors with activity on clinically relevant serine- and metallo-carbapenemases

Bacteria are known to evade β-lactam antibiotic action by producing β-lactamases (BLs), including carbapenemases, which are able to hydrolyze nearly all available β-lactams. The production of BLs represents one of the best known and most targeted mechanisms of resistance in bacteria. We have performed the parallel screening of commercially available compounds against a panel of clinically relevant BLs: class A CTX-M-15 and KPC-2, subclass B1 NDM-1 and VIM-2 MBLs, and the class C P. aeruginosa AmpC. The results show that all BLs prefer scaffolds having electron pair donors: KPC-2 is preferentially inhibited by sulfonamide and tetrazole-based derivatives, NDM-1 by compounds bearing a thiol, a thiosemicarbazide or thiosemicarbazone moiety, while VIM-2 by triazole-containing molecules. Few broad-spectrum BLs inhibitors were identified; among these, compound 40 potentiates imipenem activity against an NDM-1-producing E. coli clinical strain. The binary complexes of the two most promising compounds binding NDM-1 and VIM-2 were obtained at high resolution, providing strong insights to improve molecular docking simulations, especially regarding the interaction of MBLs with inhibitors.

Profile of Enterobacteria Resistant to Beta-Lactams

A serious emerging problem worldwide is increased antimicrobial resistance. Acquisition of coding genes for evasion methods of antimicrobial drug mechanisms characterizes acquired resistance. This phenomenon has been observed in Enterobacteriaceae family. Treatment for bacterial infections is performed with antibiotics, of which the most used are beta-lactams. The aim of this study was to correlate antimicrobial resistance profiles in Enterobacteriaceae by phenotypic methods and molecular identification of 14 beta-lactamase coding genes. In this study, 70 exclusive isolates from Brazil were used, half of which were collected in veterinary clinics or hospitals Phenotypic methodologies were used and real-time PCR was the molecular methodology used, through the Sybr Green system. Regargding the results found in the tests it was observed that 74.28% were resistant to ampicillin, 62.85% were resistant to amoxicillin associated with clavalunate. The mechanism of resistance that presented the highest expression was ESBL (17.14%). The genes studied that were detected in a greater number of species were blaGIM and blaSIM (66.66% of the samples) and the one that was amplified in a smaller number of samples was blaVIM (16.66%). Therefore, high and worrying levels of antimicrobial resistance have been found in enterobacteria, and a way to minimize the accelerated emergence of their resistance includes developing or improving techniques that generate diagnoses with high efficiency and speed.

Identification of Cisplatin and Palladium(II) Complexes as Potent Metallo-β-lactamase Inhibitors for Targeting Carbapenem-Resistant Enterobacteriaceae

The emergence and prevalence of carbapenem-resistant bacterial infection have seriously threatened the clinical use of almost all β-lactam antibacterials. The development of effective metallo-β-lactamase (MβL) inhibitors to restore the existing antibiotics efficacy is an ideal alternative. Although several types of serine-β-lactamase inhibitors have been successfully developed and used in clinical settings, MβL inhibitors are not clinically available to date. Herein, we identified that cisplatin and Pd(II) complexes are potent broad-spectrum inhibitors of the B1 and B2 subclasses of MβLs and effectively revived Meropenem efficacy against MβL-expressing bacteria in vitro. Enzyme kinetics, thermodynamics, inductively coupled plasma atomic emission spectrometry (ICP-AES), matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and site-directed mutation assays revealed that these metal complexes irreversibly inhibited NDM-1 through a novel inhibition mode involving binding to Cys208 and displacing one Zn(II) ion of the enzyme with one Pt(II) containing two NH₃'s or one Pd(II) ion. Importantly, the combination therapy of Meropenem and metal complexes significantly suppressed the development of higher-level resistance in bacteria producing NDM-1, also effectively reduced the bacterial burden in liver and spleen of mice infected by carbapenem-resistant Enterobacteriaceae producing NDM-1. These findings will offer potential lead compounds for the further development of clinically useful inhibitors targeting MβLs.

In vitro activity of imipenem/relebactam against Gram-negative ESKAPE pathogens isolated in 17 European countries: 2015 SMART surveillance programme

Objectives

Relebactam is an inhibitor of class A β-lactamases, including KPC β-lactamases, and class C β-lactamases, and is currently under clinical development in combination with imipenem. The objective of the current study was to evaluate the in vitro activity of imipenem/relebactam against Gram-negative ESKAPE pathogens (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) submitted by clinical laboratories in 17 European countries to the Study for Monitoring Antimicrobial Resistance Trends (SMART) global surveillance programme in 2015.

Methods

MICs were determined using the CLSI standard broth microdilution method and interpreted using EUCAST clinical breakpoints. Relebactam was tested at a fixed concentration of 4 mg/L in combination with doubling dilutions of imipenem. Imipenem/relebactam MICs were interpreted using breakpoints for imipenem.

Results

Rates of susceptibility to imipenem and imipenem/relebactam for isolates of P. aeruginosa (n = 1705), K. pneumoniae (n = 1591) and Enterobacter spp. (n = 772) were 72.0/94.7%, 88.7/94.8% and 95.6/96.8%, respectively. Relebactam restored imipenem susceptibility to 81.1%, 54.2% and 26.5% of imipenem-non-susceptible isolates of P. aeruginosa (n = 477), K. pneumoniae (n = 179) and Enterobacter spp. (n = 34). Most imipenem/relebactam-non-susceptible isolates carried MBLs, OXA-48 or GES carbapenemases. Relebactam did not increase the number of isolates of A. baumannii (n = 486) susceptible to imipenem.

Conclusions

Relebactam restored susceptibility to imipenem for the majority of imipenem-non-susceptible isolates of P. aeruginosa and K. pneumoniae tested as well as some isolates of imipenem-non-susceptible Enterobacter spp. Based on our results, imipenem/relebactam appears to be a promising therapeutic option for treating patients with infections caused by antimicrobial-resistant Gram-negative bacilli.

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.

Current status of countermeasures for infectious diseases and resistant microbes in the field of urology

A worldwide increase in antimicrobial-resistant microbes due to the improper use of antimicrobial agents, along with a lack of progress in developing new antimicrobials, is becoming a societal problem. Although carbapenem-resistant Enterobacteriaceae, which are resistant to carbapenem antimicrobials, first appeared in 1993, treatment options remain limited. Mechanisms behind antimicrobial resistance involve changes to microbial outer membranes, drug efflux pump abnormalities, β-lactamase production and the creation of biofilms around cell bodies. Genetic information related to these forms of antimicrobial resistance exists on chromosomes and plasmids, and when located on the latter can easily be transmitted to other strains, no matter the species, which creates a risk of antimicrobial resistance spreading exceptionally rapidly. To prevent the spread of antimicrobial resistance, the World Health Organization in 2015 published an action plan on antimicrobial resistance, based on which World Health Organization member countries have laid out specific policies and targets. Urinary tract infections are a type of healthcare-associated infection, and the sexually transmitted disease pathogen, Neisseria gonorrhoeae, has been included in a list of microbes that pose a risk to human health published by the US Centers for Disease Control and Prevention. Urologists face numerous problems when attempting to use antimicrobials properly, which is one method of dealing with antimicrobial resistance. Therefore, this article describes the current state of resistant microbes associated with urinary tract infections and countermeasures for antimicrobial resistance, including new antimicrobials.

Review on plant antimicrobials: a mechanistic viewpoint

Microbial resistance to classical antibiotics and its rapid progression have raised serious concern in the treatment of infectious diseases. Recently, many studies have been directed towards finding promising solutions to overcome these problems. Phytochemicals have exerted potential antibacterial activities against sensitive and resistant pathogens via different mechanisms of action. In this review, we have summarized the main antibiotic resistance mechanisms of bacteria and also discussed how phytochemicals belonging to different chemical classes could reverse the antibiotic resistance. Next to containing direct antimicrobial activities, some of them have exerted in vitro synergistic effects when being combined with conventional antibiotics. Considering these facts, it could be stated that phytochemicals represent a valuable source of bioactive compounds with potent antimicrobial activities.

Defining the Role of Novel β-Lactam Agents That Target Carbapenem-Resistant Gram-Negative Organisms

With the current carbapenem-resistant organism crisis, conventional approaches to optimizing pharmacokinetic-pharmacodynamic parameters are frequently inadequate, and traditional salvage agents (eg, colistin, tigecycline, etc) confer high toxicity and/or have low efficacy. However, several β-lactam agents with activity against carbapenem-resistant organisms were approved recently by the US Food and Drug Administration, and more are anticipated to be approved in the near future. The primary goal of this review is to assist infectious disease practitioners with preferentially selecting 1 agent over another when treating patients infected with a carbapenem-resistant organism. However, resistance to some of these antibiotics has already developed. Antibiotic stewardship programs can ensure that they are reserved for situations in which other options are lacking and are paramount for the survival of these agents.

Novel Mercapto Propionamide Derivatives with Potent New Delhi Metallo-β-Lactamase-1 Inhibitory Activity and Low Toxicity

The emergence and worldwide prevalence of New Delhi metallo-β-lactamase 1 (NDM-1) expressing Gram-negative bacteria with resistance against most β-lactam antibiotics pose a serious threat to human health. However, no NDM-1 inhibitors are clinically approved at present. Herein, based on the lead compound captopril, a series of compounds were designed, synthesized, and evaluated for NDM-1 inhibitory activities. All designed compounds showed single digit micromolar or submicromolar NDM-1 inhibitory activities, which were much more potent than that of captopril. Among them, compounds 14a and 14m exhibited excellent NDM-1 inhibitory activities, with IC₅₀ values of 0.10 and 0.12 μM, respectively. Further studies demonstrated that compound 14m displayed low cytotoxicity, good water solubility, high metabolic stability, and low acute toxicity in mice. Importantly, compound 14m exhibited potent synergistic antimicrobial activities with Meropenem (MEM) for the treatment of clinically isolated NDM-1-expressing strains.

Treatment of Infections Due to MDR Gram-Negative Bacteria

The treatment of multidrug-resistant Gram-negative bacteria (MDR-GNB) infections in critically ill patients presents many challenges. Since an effective treatment should be administered as soon as possible, resistance to many antimicrobial classes almost invariably reduces the probability of adequate empirical coverage, with possible unfavorable consequences. In this light, readily available patient's medical history and updated information about the local microbiological epidemiology remain critical for defining the baseline risk of MDR-GNB infections and firmly guiding empirical treatment choices, with the aim of avoiding both undertreatment and overtreatment. Rapid diagnostics and efficient laboratory workflows are also of paramount importance both for anticipating diagnosis and for rapidly narrowing the antimicrobial spectrum, with de-escalation purposes and in line with antimicrobial stewardship principles. Carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii are being reported with increasing frequencies worldwide, although with important variability across regions, hospitals and even single wards. In the past few years, new treatment options, such as ceftazidime/avibactam, meropenem/vaborbactam, ceftolozane/tazobactam, plazomicin, and eravacycline have become available, and others will become soon, which have provided some much-awaited resources for effectively counteracting severe infections due to these organisms. However, their optimal use should be guaranteed in the long term, for delaying as much as possible the emergence and diffusion of resistance to novel agents. Despite important progresses, pharmacokinetic/pharmacodynamic optimization of dosages and treatment duration in critically ill patients has still some areas of uncertainty requiring further study, that should take into account also resistance selection as a major endpoint. Treatment of severe MDR-GNB infections in critically ill patients in the near future will require an expert and complex clinical reasoning, of course taking into account the peculiar characteristics of the target population, but also the need for adequate empirical coverage and the more and more specific enzyme-level activity of novel antimicrobials with respect to the different resistance mechanisms of MDR-GNB.

In vitro activity of imipenem-relebactam against non-MBL carbapenemase-producing Klebsiella pneumoniae isolated in Greek hospitals in 2015-2016

Relebactam is a β-lactamase inhibitor of class A and class C β-lactamases, including carbapenemases. We evaluated the ability of relebactam to restore imipenem susceptibility against a collection of Klebsiella pneumoniae isolates from Greek hospitals. We tested 314 non-MBL carbapenemase-producing K. pneumoniae consecutive clinical strains isolated from unique patients at 18 hospitals in Greece, between November 2014 and December 2016. Susceptibility testing of imipenem, imipenem-relebactam, meropenem, doripenem, gentamicin, and colistin was performed using broth microdilution. Additionally, MICs of ceftazidime-avibactam, fosfomycin, and tigecycline were determined by MIC Test Strips. MICs were interpreted per EUCAST breakpoints. Imipenem-relebactam MICs were interpreted using the breakpoints proposed for imipenem. Carbapenemase genes were detected using PCR. Whole genome sequencing was performed for selected isolates. Imipenem-relebactam inhibited 98.0% of the KPC-producing isolates at ≤ 2 mg/L (MIC₅₀/₉₀, 0.25/1 mg/L) and was considerably more active than imipenem (MIC₅₀/₉₀, 32/> 64 mg/L). Reduced activity of imipenem-relebactam was rarely detected (2%) and was associated with chromosomal factors (ompK35 disruption and/or mutated ompK36). Only ceftazidime-avibactam showed in vitro activity comparable to imipenem-relebactam (99.6% susceptible). Relebactam provided only weak potentiation of imipenem activity against K. pneumoniae with class D OXA-48-like enzymes. Relebactam exhibited strong potential for restoring the in vitro activity of imipenem against KPC-producing K. pneumoniae, lowering the imipenem MIC₅₀ and MIC₉₀ from 32 to 0.25 mg/L, and from > 64 to 1 mg/L, respectively. Production of KPC carbapenemase represents the main cause of carbapenem resistance among K. pneumoniae in Greek hospitals (66.5%), and this carbapenemase appears to be very well inhibited by relebactam.

An update on antimicrobial resistance and the role of newer antimicrobial agents for Pseudomonas aeruginosa

Infections due to Pseudomonas aeruginosa is a major health concern, especially hospital-acquired infections, in critically ill individuals. Antimicrobial resistance (AMR) increases the morbidity and mortality rates associated with pseudomonal infections. In this review, we aim to address two major aspects of P. aeruginosa. The first part of the review will focus on the burden of AMR and its prevailing mechanisms seen in India, while the second part will focus on the challenges and approaches in the management with special emphasis on the role of newer antimicrobial agents.

Novel β-lactam-β-lactamase inhibitor combinations: expectations for the treatment of carbapenem-resistant Gram-negative pathogens

INTRODUCTION

The burden of antimicrobial resistance among Gram-negative bacteria is increasing and growing into a major threat of public health. Treatment options for carbapenem-resistant Enterobacteriaceae are limited and resistance rates to existing compounds are mounting. The pipeline includes only a small number of novel anti-infective agents in development or in the market with promising results against multidrug-resistant (MDR) Gram-negative. Areas covered: Herein the authors present the modern available knowledge regarding novel β-lactam-β-lactamase inhibitors, i.e. mechanisms of action, in vitro activity, current PK/PDs, clinical trials and clinical efficacy against MDR and XDR Gram-negatives, as well as toxicity issues. Expert opinion: Ceftazidime-avibactam and meropenem-vaborbactam are promising therapeutic options as both are active against Enterobacteriaceae producing ESBL, AmpC, and KPC, whereas only avibactam inhibits certain class D β-lactamases, mainly OXA-48. New drugs active against Gram-negative MDR isolates including imipenem/cilastatin with relebactam and avibactam combined with aztreonam or ceftaroline are in different stages of development. However, the disadvantage to be seriously considered by the clinician is that β-lactam/β-lactamase inhibitors are ineffective against metallo-β-lactamases (with the exception of aztreonam-avibactam) as well as Acinetobacter baumannii.

The Reaction Mechanism of Metallo-β-Lactamases Is Tuned by the Conformation of an Active-Site Mobile Loop

Carbapenems are "last resort" β-lactam antibiotics used to treat serious and life-threatening health care-associated infections caused by multidrug-resistant Gram-negative bacteria. Unfortunately, the worldwide spread of genes coding for carbapenemases among these bacteria is threatening these life-saving drugs. Metallo-β-lactamases (MβLs) are the largest family of carbapenemases. These are Zn(II)-dependent hydrolases that are active against almost all β-lactam antibiotics. Their catalytic mechanism and the features driving substrate specificity have been matter of intense debate. The active sites of MβLs are flanked by two loops, one of which, loop L3, was shown to adopt different conformations upon substrate or inhibitor binding, and thus are expected to play a role in substrate recognition. However, the sequence heterogeneity observed in this loop in different MβLs has limited the generalizations about its role. Here, we report the engineering of different loops within the scaffold of the clinically relevant carbapenemase NDM-1. We found that the loop sequence dictates its conformation in the unbound form of the enzyme, eliciting different degrees of active-site exposure. However, these structural changes have a minor impact on the substrate profile. Instead, we report that the loop conformation determines the protonation rate of key reaction intermediates accumulated during the hydrolysis of different β-lactams in all MβLs. This study demonstrates the existence of a direct link between the conformation of this loop and the mechanistic features of the enzyme, bringing to light an unexplored function of active-site loops on MβLs.

Imipenem-Relebactam and Meropenem-Vaborbactam: Two Novel Carbapenem-β-Lactamase Inhibitor Combinations

Relebactam (formerly known as MK-7655) is a non-β-lactam, bicyclic diazabicyclooctane, β-lactamase inhibitor that is structurally related to avibactam, differing by the addition of a piperidine ring to the 2-position carbonyl group. Vaborbactam (formerly known as RPX7009) is a non-β-lactam, cyclic, boronic acid-based, β-lactamase inhibitor. The structure of vaborbactam is unlike any other currently marketed β-lactamase inhibitor. Both inhibitors display activity against Ambler class A [including extended-spectrum β-lactamases (ESBLs), Klebsiella pneumoniae carbapenemases (KPCs)] and class C β-lactamases (AmpC). Little is known about the potential for relebactam or vaborbactam to select for resistance; however, inactivation of the porin protein OmpK36 in K. pneumoniae has been reported to confer resistance to both imipenem-relebactam and meropenem-vaborbactam. The addition of relebactam significantly improves the activity of imipenem against most species of Enterobacteriaceae [by lowering the minimum inhibitory concentration (MIC) by 2- to 128-fold] depending on the presence or absence of β-lactamase enzymes. Against Pseudomonas aeruginosa, the addition of relebactam also improves the activity of imipenem (MIC reduced eightfold). Based on the data available, the addition of relebactam does not improve the activity of imipenem against Acinetobacter baumannii, Stenotrophomonas maltophilia and most anaerobes. Similar to imipenem-relebactam, the addition of vaborbactam significantly (2- to > 1024-fold MIC reduction) improves the activity of meropenem against most species of Enterobacteriaceae depending on the presence or absence of β-lactamase enzymes. Limited data suggest that the addition of vaborbactam does not improve the activity of meropenem against A. baumannii, P. aeruginosa, or S. maltophilia. The pharmacokinetics of both relebactam and vaborbactam are described by a two-compartment, linear model and do not appear to be altered by the co-administration of imipenem and meropenem, respectively. Relebactam's approximate volume of distribution (V _d) and elimination half-life (t _½) of ~ 18 L and 1.2-2.1 h, respectively, are similar to imipenem. Likewise, vaborbactam's V _d and t_½ of ~ 18 L and 1.3-2.0 h, respectively, are comparable to meropenem. Like imipenem and meropenem, relebactam and vaborbactam are both primarily renally excreted, and clearance correlates with creatinine clearance. In vitro and in vivo pharmacodynamic studies have reported bactericidal activity for imipenem-relebactam and meropenem-vaborbactam against various Gram-negative β-lactamase-producing bacilli that are not inhibited by their respective carbapenems alone. These data also suggest that pharmacokinetic-pharmacodynamic parameters correlating with efficacy include time above the MIC for the carbapenems and overall exposure for their companion β-lactamase inhibitors. Phase II clinical trials to date have reported that imipenem-relebactam is as effective as imipenem alone for treatment of complicated intra-abdominal infections and complicated urinary tract infections, including acute pyelonephritis. Imipenem-relebactam is currently in two phase III clinical trials for the treatment of imipenem-resistant bacterial infections, as well as hospital-associated bacterial pneumonia (HABP) and ventilator-associated bacterial pneumonia (VABP). A phase III clinical trial has reported superiority of meropenem-vaborbactam over piperacillin-tazobactam for the treatment of complicated urinary tract infections, including acute pyelonephritis. Meropenem-vaborbactam has recently demonstrated higher clinical cure rates versus best available therapy for the treatment of carbapenem-resistant Enterobacteriaceae (CRE), as well as for HABP and VABP. The safety and tolerability of imipenem-relebactam and meropenem-vaborbactam has been reported in various phase I pharmacokinetic studies and phase II and III clinical trials. Both combinations appear to be well tolerated in healthy subjects and hospitalized patients, with few serious drug-related treatment-emergent adverse events reported to date. In conclusion, relebactam and vaborbactam serve to broaden the spectrum of imipenem and meropenem, respectively, against β-lactamase-producing Gram-negative bacilli. The exact roles for imipenem-relebactam and meropenem-vaborbactam will be defined by efficacy and safety data from further clinical trials. Potential roles in therapy for these agents include the treatment of suspected or documented infections caused by resistant Gram-negative bacilli-producing ESBL, KPC, and/or AmpC β-lactamases. The usage of these agents in patients with CRE infections will likely become the standard of care. Finally, increased activity of imipenem-relebactam against P. aeruginosa may be of clinical benefit to patients with suspected or documented P. aeruginosa infections.

The Infinity War: How to Cope with Carbapenem-resistant Enterobacteriaceae

Carbapenem-resistant Enterobacteriaceae (CRE) are now spread worldwide. In Korea, the number of CRE isolation is rapidly increasing, and impending endemicity is a concern. To cope well with CRE, thorough infection control, such as active surveillance, early detection, strict contact precaution, cleaning the environment, and antibiotic stewardship is very important. Therapeutic options include polymyxin, tigecycline, fosfomycin or the combination of them with carbapenem, which is currently the mainstay of treatment. In addition, various combination regimens with new carbapenemase inhibitors such as avibactam, vaborbactam, or relebactam, and other classes of antimicrobials such as plazomicin and siderophore cephalosporin are in the process of evaluation.

Class A β-lactamases and inhibitors: In silico analysis of the binding mode and the relationship with resistance

β-lactams are one of the most common antimicrobials used to treat bacterial infections. However, bacterial resistance has compromised their efficacy, mainly due to the β-lactamase enzyme production. To overcome this resistance, β-lactamase inhibitors can be used in association with these antimicrobials. Herein, we analyzed the structural characteristics of β-lactamases and their interactions with classical inhibitors, such as clavulanic acid (CA), sulbactam (SB) and tazobactam (TZ) to gain insights into resistance. The homology models of five class A β-lactamases, namely CARB-3, IMI-1, SFO-1, SHV-5 and TEM-10, were constructed and validated and revealed an overall 3D structural conservation, but with significant differences in the electrostatic potential maps, especially at important regions in the catalytic site. Molecular dockings of CA, SB and TZ with these enzymes revealed a covalent bond with the S70 in all complexes, except Carb-3 which is in agreement with experimental data reported so far. This is likely related to the less voluminous active site of Carb-3 model. Although few specific contacts were observed in the β-lactamase-inhibitor complexes, all compounds interacted with the residues in positions 73, 130, 132, 236 and 237. Therefore, this study provides new perspectives for the design of innovative compounds with broad-spectrum inhibitory profiles against β-lactamases.

Activity of imipenem/relebactam against Pseudomonas aeruginosa with antimicrobial-resistant phenotypes from seven global regions: SMART 2015-2016

OBJECTIVES

Relebactam inhibits Ambler class A and C β-lactamases. Imipenem/relebactam has completed one phase 3 clinical study of patients infected with imipenem-non-susceptible Gram-negative bacilli. Two more phase 3 clinical studies are in progress for the treatment of patients with hospital-acquired and ventilator-associated bacterial pneumonia, complicated intra-abdominal infections and complicated urinary tract infections. In the current study, clinical Pseudomonas aeruginosa isolates cultured by medical centre laboratories in seven geographic regions (Africa, Asia, Europe, Latin America, Middle East, USA/Canada, South Pacific) were tested for susceptibility to imipenem/relebactam and comparators.

METHODS

A total of 12170 isolates collected as part of the 2015-2016 Study for Monitoring Antimicrobial Resistance Trends (SMART) global surveillance program were tested using the Clinical and Laboratory Standards Institute (CLSI)-defined broth microdilution method. Relebactam was tested at a fixed concentration of 4μg/mL in combination with doubling dilutions of imipenem. Imipenem/relebactam MICs were interpreted using current CLSI breakpoints for imipenem.

RESULTS

At the imipenem susceptible breakpoint (≤2μg/mL), imipenem/relebactam inhibited 90.8% of all P. aeruginosa isolates and 70.7% of multidrug-resistant (MDR) isolates (n=3708). Relebactam restored imipenem susceptibility to 70.3% (2656/3776) of imipenem-non-susceptible isolates and increased percent susceptibility to imipenem against isolates with ceftazidime-non-susceptible (by 35.2%), piperacillin/tazobactam-non-susceptible (by 36.6%), cefepime-non-susceptible (by 36.8%) and MDR (by 41.9%) phenotypes. Across the seven geographic regions studied, susceptibility to imipenem/relebactam ranged from 84.0% (Latin America) to 96.0% (South Pacific).

CONCLUSIONS

Imipenem/relebactam could provide an important treatment option against infections with P. aeruginosa isolates that are non-susceptible to several currently available antipseudomonal β-lactams.

In Vitro Activity of Imipenem-Relebactam against Clinical Isolates of Gram-Negative Bacilli Isolated in Hospital Laboratories in the United States as Part of the SMART 2016 Program

Relebactam is a non-β-lactam, bicyclic diazabicyclooctane β-lactamase inhibitor of class A and class C β-lactamases, including Klebsiella pneumoniae carbapenemases (KPCs). It is in phase 3 clinical development in combination with imipenem/cilastatin. The in vitro activities of imipenem-relebactam, imipenem, and comparators were determined using the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution method for isolates of Enterobacteriaceae (n = 3,419) and Pseudomonas aeruginosa (n = 896) collected in 2016 by 21 U.S. hospital laboratories participating in the SMART (Study for Monitoring Antimicrobial Resistance Trends) global surveillance program. Relebactam was tested at a fixed concentration of 4 μg/ml. Imipenem-relebactam MICs were interpreted using CLSI breakpoints for imipenem. Rates of susceptibility to imipenem-relebactam and imipenem for non-ProteeaeEnterobacteriaceae (n = 3,143) and P. aeruginosa were 99.1% (3,115/3,143) and 95.9% (3,013/3,143) and were 94.4% (846/896) and 74.7% (669/896), respectively. Relebactam restored imipenem susceptibility to 78.5% (102/130) of imipenem-nonsusceptible non-ProteeaeEnterobacteriaceae and to 78.0% (177/227) of imipenem-nonsusceptible P. aeruginosa isolates. Susceptibility to imipenem-relebactam was 98.2% (444/452) and 82.2% (217/264) for multidrug-resistant (MDR) non-ProteeaeEnterobacteriaceae and MDR P. aeruginosa, respectively. Given the ability of relebactam to restore susceptibility to imipenem in nonsusceptible isolates of both non-ProteeaeEnterobacteriaceae and P. aeruginosa and to demonstrate potent activity against current MDR isolates of both non-ProteeaeEnterobacteriaceae and P. aeruginosa, further development of imipenem-relebactam appears warranted.

Inhibitors of Selected Bacterial Metalloenzymes

The utilization of bacterial metalloenzymes, especially ones not having mammalian (human) counterparts, has drawn attention to develop novel antibacterial agents to overcome drug resistance and especially multidrug resistance. In this review, we focus on the recent achievements on the development of inhibitors of bacterial enzymes peptide deformylase (PDF), metallo-β-lactamase (MBL), methionine aminopeptidase (MetAP) and UDP-3-O-acyl- N-acetylglucosamine deacetylase (LpxC). The state of the art of the design and investigation of inhibitors of bacterial metalloenzymes is presented, and challenges are outlined and discussed.

Challenges in the Development of a Thiol-Based Broad-Spectrum Inhibitor for Metallo-β-Lactamases

Pathogens, expressing metallo-β-lactamases (MBLs), become resistant against most β-lactam antibiotics. Besides the dragging search for new antibiotics, development of MBL inhibitors would be an alternative weapon against resistant bacterial pathogens. Inhibition of resistance enzymes could restore the antibacterial activity of β-lactams. Various approaches to MBL inhibitors are described; among others, the promising motif of a zinc coordinating thiol moiety is very popular. Nevertheless, since the first report of a thiol-based MBL inhibitor (thiomandelic acid) in 2001, no steps in development of thiol based MBL inhibitors were reported that go beyond clinical isolate testing. In this study, we report on the synthesis and biochemical characterization of thiol-based MBL inhibitors and highlight the challenges behind the development of thiol-based compounds, which exhibit good in vitro activity toward a broad spectrum of MBLs, selectivity against human off-targets, and reasonable activity against clinical isolates.

Bismuth antimicrobial drugs serve as broad-spectrum metallo-β-lactamase inhibitors

Drug-resistant superbugs pose a huge threat to human health. Infections by Enterobacteriaceae producing metallo-β-lactamases (MBLs), e.g., New Delhi metallo-β-lactamase 1 (NDM-1) are very difficult to treat. Development of effective MBL inhibitors to revive the efficacy of existing antibiotics is highly desirable. However, such inhibitors are not clinically available till now. Here we show that an anti-Helicobacter pylori drug, colloidal bismuth subcitrate (CBS), and related Bi(III) compounds irreversibly inhibit different types of MBLs via the mechanism, with one Bi(III) displacing two Zn(II) ions as revealed by X-ray crystallography, leading to the release of Zn(II) cofactors. CBS restores meropenem (MER) efficacy against MBL-positive bacteria in vitro, and in mice infection model, importantly, also slows down the development of higher-level resistance in NDM-1-positive bacteria. This study demonstrates a high potential of Bi(III) compounds as the first broad-spectrum B1 MBL inhibitors to treat MBL-positive bacterial infection in conjunction with existing carbapenems.

Dissemination and Characteristics of a Novel Plasmid-Encoded Carbapenem-Hydrolyzing Class D β-Lactamase, OXA-436, Found in Isolates from Four Patients at Six Different Hospitals in Denmark

The diversity of OXA-48-like carbapenemases is continually expanding. In this study, we describe the dissemination and characteristics of a novel carbapenem-hydrolyzing class D β-lactamase (CHDL) named OXA-436. In total, six OXA-436-producing Enterobacteriaceae isolates, including Enterobacter asburiae (n = 3), Citrobacter freundii (n = 2), and Klebsiella pneumoniae (n = 1), were identified in four patients in the period between September 2013 and April 2015. All three species of OXA-436-producing Enterobacteriaceae were found in one patient. The amino acid sequence of OXA-436 showed 90.4 to 92.8% identity to the amino acid sequences of other acquired OXA-48-like variants. Expression of OXA-436 in Escherichia coli and kinetic analysis of purified OXA-436 revealed an activity profile similar to that of OXA-48 and OXA-181, with activity against penicillins, including temocillin; limited or no activity against extended-spectrum cephalosporins; and activity against carbapenems. The bla_OXA-436 gene was located on a conjugative ∼314-kb IncHI2/IncHI2A plasmid belonging to plasmid multilocus sequence typing sequence type 1 in a region surrounded by chromosomal genes previously identified to be adjacent to bla_OXA genes in Shewanella spp. In conclusion, OXA-436 is a novel CHDL with functional properties similar to those of OXA-48-like CHDLs. The described geographical spread among different Enterobacteriaceae and the plasmid location of bla_OXA-436 illustrate its potential for further dissemination.

In Vitro Activity of Imipenem-Relebactam against Gram-Negative ESKAPE Pathogens Isolated by Clinical Laboratories in the United States in 2015 (Results from the SMART Global Surveillance Program)

Relebactam (formerly MK-7655) is an inhibitor of class A and C β-lactamases, including Klebsiella pneumoniae carbapenemase (KPC), and is currently in clinical development in combination with imipenem-cilastatin. Using Clinical and Laboratory Standards Institute (CLSI)-defined broth microdilution methodology, we evaluated the in vitro activities of imipenem-relebactam, imipenem, and seven routinely tested parenteral antimicrobial agents against Gram-negative ESKAPE pathogens (including Klebsiella pneumoniae, n = 689; Acinetobacter baumannii, n = 72; Pseudomonas aeruginosa, n = 845; and Enterobacter spp., n = 399) submitted by 21 clinical laboratories in the United States in 2015 as part of the SMART (Study for Monitoring Antimicrobial Resistance Trends) global surveillance program. Relebactam was tested at a fixed concentration of 4 μg/ml in combination with doubling dilutions of imipenem. Imipenem-relebactam MICs were interpreted using CLSI imipenem breakpoints. The respective rates of susceptibility to imipenem-relebactam and imipenem were 94.2% (796/845) and 70.3% (594/845) for P. aeruginosa, 99.0% (682/689) and 96.1% (662/689) for K. pneumoniae, and 100% (399/399) and 98.0% (391/399) for Enterobacter spp. Relebactam restored imipenem susceptibility to 80.5% (202/251), 74.1% (20/27), and 100% (8/8) of isolates of imipenem-nonsusceptible P. aeruginosa, K. pneumoniae, and Enterobacter spp. Relebactam did not increase the number of isolates of Acinetobacter spp. susceptible to imipenem, and the rates of resistance to all of the agents tested against this pathogen were >30%. Further development of imipenem-relebactam is warranted given the demonstrated ability of relebactam to restore the activity of imipenem against current clinical isolates of Enterobacteriaceae and P. aeruginosa that are nonsusceptible to carbapenems and its potential as a therapy for treating patients with antimicrobial-resistant Gram-negative infections.

Invitro activity of imipenem-relebactam against gram-negative bacilli isolated from patients with lower respiratory tract infections in the United States in 2015 - Results from the SMART global surveillance program

The β-lactamase inhibitor relebactam inactivates class A β-lactamases, including KPC-type carbapenemases, and class C β-lactamases. Relebactam combined with imipenem is in clinical development for several indications, including hospital-acquired and ventilator-associated pneumonia. Employing CLSI-defined broth microdilution methodology, we evaluated the activities of imipenem-relebactam (using imipenem MIC breakpoints) and comparators against non-Proteeae Enterobacteriaceae (n=853) and Pseudomonas aeruginosa (n=598) isolated from lower respiratory tract infection samples in 20 hospital laboratories in the United States participating in the 2015 SMART (Study for Monitoring Antimicrobial Resistance Trends) global surveillance program. Imipenem-relebactam and imipenem susceptibilities were 97.2% and 91.6% for non-Proteeae Enterobacteriaceae and 93.1% and 68.1% for P. aeruginosa. Relebactam restored imipenem susceptibility to 66.7% and 78.5% of imipenem-non-susceptible non-Proteeae Enterobacteriaceae isolates (n=72) and P. aeruginosa (n=191), respectively. Further development of imipenem-relebactam as therapy for lower respiratory tract infections is warranted given relebactam's ability to restore activity to imipenem against non-susceptible non-Proteeae Enterobacteriaceae and P. aeruginosa.

Identification and Characterization of the Sulfazecin Monobactam Biosynthetic Gene Cluster

The monobactams, exemplified by the natural product sulfazecin, are the only class of β-lactam antibiotics not inactivated by metallo-β-lactamases, which confer bacteria with extended-spectrum β-lactam resistance. We screened a transposon mutagenesis library from Pseudomonas acidophila ATCC 31363 and isolated a sulfazecin-deficient mutant that revealed a gene cluster encoding two non-ribosomal peptide synthetases (NRPSs), a methyltransferase, a sulfotransferase, and a dioxygenase. Three modules and an aberrant C-terminal thioesterase (TE) domain are distributed across the two NRPSs. Biochemical examination of the adenylation (A) domains provided evidence that L-2,3-diaminopropionate, not L-serine as previously thought, is the direct source of the β-lactam ring of sulfazecin. ATP/PPi exchange assay also revealed an unusual substrate selectivity shift of one A domain when expressed with or without the immediately upstream condensation domain. Gene inactivation analysis defined a cluster of 13 open reading frames sufficient for sulfazecin production, precursor synthesis, self-resistance, and regulation. The identification of a key intermediate supported a proposed NRPS-mediated mechanism of sulfazecin biosynthesis and β-lactam ring formation distinct from the nocardicins, another NRPS-derived subclass of monocyclic β-lactam. These findings will serve as the basis for further biosynthetic research and potential engineering of these important antibiotics.

Probing minority population of antibiotic-resistant bacteria

The evolution and spread of antibiotic-resistant pathogens has become a major threat to public health. Advanced tools are urgently needed to quickly diagnose antibiotic-resistant infections to initiate appropriate treatment. Here we report the development of a highly sensitive flow cytometric method to probe minority population of antibiotic-resistant bacteria via single cell detection. Monoclonal antibody against TEM-1 β-lactamase and Alexa Fluor 488-conjugated secondary antibody were used to selectively label resistant bacteria green, and nucleic acid dye SYTO 62 was used to stain all the bacteria red. A laboratory-built high sensitivity flow cytometer (HSFCM) was applied to simultaneously detect the side scatter and dual-color fluorescence signals of single bacteria. By using E. coli JM109/pUC19 and E. coli JM109 as the model systems for antibiotic-resistant and antibiotic-susceptible bacteria, respectively, as low as 0.1% of antibiotic-resistant bacteria were accurately quantified. By monitoring the dynamic population change of a bacterial culture with the administration of antibiotics, we confirmed that under the antimicrobial pressure, the original low population of antibiotic-resistant bacteria outcompeted susceptible strains and became the dominant population after 5hours of growth. Detection of antibiotic-resistant infection in clinical urine samples was achieved without cultivation, and the bacterial load of susceptible and resistant strains can be faithfully quantified. Overall, the HSFCM-based quantitative method provides a powerful tool for the fundamental studies of antibiotic resistance and holds the potential to provide rapid and precise guidance in clinical therapies.

Endless Resistance. Endless Antibiotics?

The practice of medicine was profoundly transformed by the introduction of the antibiotics (compounds isolated from Nature) and the antibacterials (compounds prepared by synthesis) for the control of bacterial infection. As a result of the extraordinary success of these compounds over decades of time, a timeless biological activity for these compounds has been presumed. This presumption is no longer. The inexorable acquisition of resistance mechanisms by bacteria is retransforming medical practice. Credible answers to this dilemma are far better recognized than they are being implemented. In this perspective we examine (and in key respects, reiterate) the chemical and biological strategies being used to address the challenge of bacterial resistance.

A telescopic one-pot synthesis of β-lactam rings using amines as a convenient source of imines

A facile synthetic approach to substituted β-lactams was designed, using secondary benzylic amines and acid chlorides as starting materials. The reactions proceeded smoothly and all the products were obtained in good yields.