Structure-based virtual screening, molecular docking, and molecular dynamics simulation approaches for identification of new potential inhibitors of class a β-lactamase enzymes

Bacteria are smart organisms that create drug resistance by decreasing the effect of antibiotics in different ways, such as secretion of the β-lactamase enzymes. Finding the compounds that can act as the inhibitors of these enzymes is a great help in reducing drug resistance and treat all types of infections. In this study, using molecular docking and molecular dynamics simulation techniques, we introduced two Relebactam substructures as new inhibitors of class A β-lactamase enzymes. Results of molecular docking show that the conformation of these two compounds in the active site of class A β-lactamase enzymes has a good match with Relebactam and their binding affinity to enzymes is equal to or better than Relebactam. Results showed a good tendency for binding and the formation of van der Waals and hydrogen interactions between the desired compounds and the β-lactamase enzymes. The results of the analysis of the molecular dynamics simulation trajectories showed that in the presence of the desired compounds, the second structures of the enzymes did not undergo many changes and in none of the systems, the binding of the compounds to the enzyme did not cause much instability, and in most cases made the structure stable. The hydrogen bonds were stable during the simulation time and in most cases, the new compounds formed more hydrogen bonds and had better binding affinity than Relebactam confirms the docking results. The results of this study can be helpful in designing new beta-lactamase inhibitors and new treatment methods to deal with drug resistance.Communicated by Ramaswamy H. Sarma.

Favourable effect of clavulanic acid on the minimum inhibitory concentrations of cefixime and ceftibuten in ESBL-producing Escherichia coli and Klebsiella pneumoniae

OBJECTIVES

The use of cephalosporins combined with clavulanate for the treatment of ESBL-harbouring Enterobacteriaceae has been scarcely described. We aimed to describe the effect of different concentrations of clavulanate in the MIC of cefixime and ceftibuten of ESBL-producing Escherichia coli and Klebsiella pneumoniae.

METHODS

ESBL-producing E. coli and K. pneumoniae isolates were studied. Fixed concentrations of cefixime and ceftibuten (ranges of 32-0.25 and 64-0.5 ng/ml, respectively) were used. Combinations of cefixime/clavulanate and ceftibuten/clavulanate in different ratios (1:0, 1:1, 2:1, 4:1, 8:1, 16:1, 32:1) were tested. MIC were determined by broth microdilution.

RESULTS

A total of 6 ESBL-producing E. coli, 6 ESBL-producing K. pneumoniae and 2 control E. coli were tested. When different quantities of clavulanate were added to cefixime and ceftibuten, greater than two-fold decreases in the MIC were observed. When testing the 1:1 cefixime/clavulanate ratio, 10/12 isolates were susceptible. When the ratios 2:1, 4:1, 8:1 and 16:1 were tested, susceptibility was noted for 9/12, 8/12, 4/12 and 5/12 isolates, respectively. Only 2/12 K. pneumoniae isolates were susceptible when the ratio 32:1 was tested. When testing ceftibuten/clavulanate, all isolates remained susceptible across all experiments.

CONCLUSIONS

Clavulanic acid has a favourable effect in reducing the MIC of cefixime and ceftibuten in isolates of ESBL-producing E. coli and K. pneumoniae. Combining clavulanate with ceftibuten or cefixime could be a useful treatment strategy.

Aurones and derivatives as promising New Delhi metallo-β-lactamase (NDM-1) inhibitors

Bacterial resistance is undoubtedly one of the main public health concerns especially with the emergence of metallo-β-lactamases (MBLs) able to hydrolytically inactivate β-lactam antibiotics. Currently, there are no inhibitors of MBLs in clinical use to rescue antibiotic action and the New Delhi metallo-β-lactamase-1 (NDM-1) is still considered as one of the most relevant targets for inhibitor development. Following a fragment-based strategy to find new NDM-1 inhibitors, we identified aurone as a promising scaffold. A series of 60 derivatives were then evaluated and two of them were identified as promising inhibitors with Ki values as low as 1.7 and 2.5 µM. Moreover, these two most active compounds were able to potentiate meropenem in in vitro antimicrobial susceptibility assays. The molecular modelling provided insights about their likely interactions with the active site of NDM-1, thus enabling further improvement in the structure of this new inhibitor family.

Characterization of a novel inhibitor for the New Delhi metallo-β-lactamase-4: Implications for drug design and combating bacterial drug resistance

The bacterial metallo-β-lactamases (MBLs) catalyze the inactivation of β-lactam antibiotics. Identifying novel pharmacophores remains crucial for the clinical development of additional MBL inhibitors. Previously, 1-hydroxypyridine-2(1H)-thione-6-carboxylic acid, hereafter referred to as 1,2-HPT-6-COOH, was reported as a low cytotoxic nanomolar β-lactamase inhibitor of Verona-integron-encoded metallo-β-lactamase 2, capable of rescuing β-lactam antibiotic activity. In this study, we explore its exact mechanism of inhibition and the extent of its activity through structural characterization of its binding to New Delhi metallo-β-lactamase 4 (NDM-4) and its inhibitory activity against both NDM-1 and NDM-4. Of all the structure-validated MBL inhibitors available, 1,2-HPT-6-COOH is the first discovered compound capable of forming an octahedral coordination sphere with Zn2 of the binuclear metal center. This unexpected mechanism of action provides important insight for the further optimization of 1,2-HPT-6-COOH and the identification of additional pharmacophores for MBL inhibition.

The activity and mechanism of vidofludimus as a potent enzyme inhibitor against NDM-1-positive E. coli

New Delhi metallo-β-lactamase-1 (NDM-1) is the most important and prevalent enzyme among all metallo-β-lactamases. NDM-1 can hydrolyze almost all-available β-lactam antibiotics including carbapenems, resulting in multidrug resistance, which poses an increasing clinical threat. However, there is no NDM-1 inhibitor approved for clinical treatment. Therefore, identifying a novel and potential enzyme inhibitor against NDM-1-mediated infections is an urgent need. In this study, vidofludimus was identified as a potential NDM-1 inhibitor by structure-based virtual screening and an enzyme activity inhibition assay. Vidofludimus significantly inhibited NDM-1 hydrolysis activity with a significant dose-dependent effect. When the vidofludimus concentration was 10 μg/ml, the inhibition rate and 50% inhibitory concentration were 93.3% and 13.8 ± 0.5 μM, respectively. In vitro, vidofludimus effectively restored the antibacterial activity of meropenem against NDM-1-positive Escherichia coli (E. coli), and the minimum inhibitory concentration of meropenem was decreased from 64 μg/ml to 4 μg/ml, a 16-fold reduction. The combination of vidofludimus and meropenem showed a significant synergistic effect with a fractional inhibitory concentration index of 0.125 and almost all the NDM-1-positive E. coli were killed within 12 h. Furthermore, the synergistic therapeutic effect of vidofludimus and meropenem in vivo was evaluated in mice infected with NDM-1 positive E. coli. Compared with the control treatment, vidofludimus combined with meropenem significantly improved the survival rate of mice infected with NDM-1-positive E. coli (P < 0.05), decreased the white blood cell count, the bacterial burden and inflammatory response induced by NDM-1-positive E. coli (P < 0.05), and alleviated histopathological damage in infected mice. It was demonstrated by molecular dynamic simulation, site-directed mutagenesis and biomolecular interaction that vidofludimus could interact directly with the key amino acids (Met67, His120, His122 and His250) and Zn²⁺ in the active site of NDM-1, thereby competitively inhibiting the hydrolysis activity of NDM-1 on meropenem. In summary, vidofludimus holds promise as anNDM-1 inhibitor, and the combination of vidofludimus and meropenem has potential as a therapeutic strategy for NDM-1-mediated infections.

Ceftolozane-Tazobactam Pharmacokinetics in the Abdominal Tissue of Patients Undergoing Lower Gastrointestinal Surgery: Dosing Considerations Based on Site-Specific Pharmacodynamic Target Attainment

INTRODUCTION

Recently, complicated intra-abdominal infections (cIAI) have been caused not only by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa, but also by extended-spectrum β-lactamase-producing Enterobacterales members. Ceftolozane-tazobactam (CTLZ-TAZ) is considered to exhibit therapeutic effects against cIAI. Studies on the concentrations of antibiotics in abdominal tissues directly affected by cIAI are limited. Therefore, in this study, we investigated the pharmacokinetics of CTLZ-TAZ in abdominal tissue and simulated the administration regimen required to achieve the pharmacodynamic target for cIAI-causing bacteria.

METHODS

Patients scheduled for elective lower gastrointestinal surgery were intravenously administered preoperative CTLZ-TAZ (1 g CTLZ and 0.5 g TAZ). Plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue samples were collected during the surgery, and CTLZ as well as TAZ concentrations were measured. The noncompartmental and compartmental pharmacokinetic parameters were then estimated. Site-specific pharmacodynamic target attainment analysis using 1.5 g of CTLZ-TAZ was performed.

RESULTS

CTLZ-TAZ was administered to nine patients (once to five patients and twice to four patients). The mean peritoneal fluid-to-plasma ratio (one dose/two doses) for CTLZ was 0.74/1.15, which was slightly higher than the mean peritoneal fluid-to-plasma ratio for TAZ (0.95/1.13). The ratio for subcutaneous adipose was lower than those for peritoneal fluid and peritoneum tissues. We also discovered that the average ratio of CTLZ and TAZ concentrations in all tissues was maintained at or above 2:1. In our investigation of pharmacodynamic target attainment in each tissue, the desired bactericidal effect was attained with all CTLZ-TAZ (1.5 g) administration regimens [q12h (3 g/day), q8h (4.5 g/day), and q6h (6 g/day)].

CONCLUSION

To the best of our knowledge, this is the first study investigating the optimal pharmacodynamic level of CTLZ-TAZ in the abdominal tissue against cIAI-causing bacteria. This study also serves as a guideline for designing an optimal administration regimen based on pharmacodynamic target attainment for cIAI-causing bacteria.

DETAILS OF THE TRIAL REGISTRATION

The institutional review board of Hiroshima University Hospital, CRB6180006. The Japan Registry of Clinical Trials, jRCTs061190025.

Exploring the Antibiotic Resistance Profile of Clinical Klebsiella pneumoniae Isolates in Portugal

While antibiotic resistance is rising to dangerously high levels, resistance mechanisms are spreading globally among diverse bacterial species. The emergence of antibiotic-resistant Klebsiella pneumoniae, mainly due to the production of antibiotic-inactivating enzymes, is currently responsible for most treatment failures, threatening the effectiveness of classes of antibiotics used for decades. This study assessed the presence of genetic determinants of β-lactam resistance in 102 multi-drug resistant (MDR) K. pneumoniae isolates from patients admitted to two central hospitals in northern Portugal from 2010 to 2020. Antimicrobial susceptibility testing revealed a high rate (>90%) of resistance to most β-lactam antibiotics, except for carbapenems and cephamycins, which showed antimicrobial susceptibility rates in the range of 23.5−34.3% and 40.2−68.6%, respectively. A diverse pool of β-lactam resistance genetic determinants, including carbapenemases- (i.e., blaKPC-like and blaOXA-48-like), extended-spectrum β-lactamases (ESBL; i.e., blaTEM-like, blaCTX-M-like and blaSHV-like), and AmpC β-lactamases-coding genes (i.e., blaCMY-2-like and blaDHA-like) were found in most K. pneumoniae isolates. blaKPC-like (72.5%) and ESBL genes (37.3−74.5%) were the most detected, with approximately 80% of K. pneumoniae isolates presenting two or more resistance genes. As the optimal treatment of β-lactamase-producing K. pneumoniae infections remains problematic, the high co-occurrence of multiple β-lactam resistance genes must be seen as a serious warning of the problem of antimicrobial resistance.

Design, Synthesis, and Biological Evaluation of New 1H-Imidazole-2-Carboxylic Acid Derivatives as Metallo-β-Lactamase Inhibitors

As one of important mechanisms to β-lactam antimicrobial resistance, metallo-β-lactamases (MBLs) have been receiving increasing worldwide attentions. Ambler subclass B1 MBLs are most clinically relevant, because they can hydrolyze almost all β-lactams with the exception of monobactams. However, it is still lacking of clinically useful drugs to combat MBL-medicated resistance. We previously identified 1H-imidazole-2-carboxylic acid as a core metal-binding pharmacophore (MBP) to target multiple B1 MBLs. Herein, we report structural optimization of 1H-imidazole-2-carboxylic acid and substituents. Structure-activity relationship (SAR) analyses revealed that replacement of 1H-imidazole-2-carboxylic acid with other structurally highly similar MBPs excepting thiazole-4-carboxylic acid resulted in decreased MBL inhibition. Further SAR studies identified more potent inhibitors to MBLs, of which 28 manifested IC₅₀ values of 0.018 µM for both VIM-2 and VIM-5. The microbiological tests demonstrated that the most tested compounds showed improved synergistic effects; some compounds at 1 µg/ml were able to reduce meropenem MIC by at least 16-fold, which will be worth further development of new potent inhibitors particularly targeting VIM-type MBLs.

Molecular Characterization of Extended Spectrum β-Lactamase (ESBL) and Virulence Gene-Factors in Uropathogenic Escherichia coli (UPEC) in Children in Duhok City, Kurdistan Region, Iraq

Background: The presence of extended-spectrum β-lactamase (ESBL)-producing bacteria among uropathogens is significantly increasing in children all over the world. Thus, this research was conducted to investigate the prevalence of E. coli and their antimicrobial susceptibility pattern, and both genes of ESBL-producing E. coli resistant and virulence factor in UTIs patients among children in Duhok Province, Kurdistan, Iraq. Method: a total of 67 E. coli were identified from 260 urine samples of pediatric patients diagnosed with UTIs aged (0−15 years) which were collected from Heevi Pediatric Teaching Hospital, from August 2021 to the end of February 2022. Result: a high proportion of UPEC infections at ages <5 years and the rates among girls (88%) were significantly higher than those among the boys. A wide variety of E. coli are resistant to most antibiotics, such as Amoxicillin, Ampicillin and Tetracycline, and 64% of them were positive for ESBL. Interestingly, the presence of both the ESBL marker genes (blaTEM, and blaCTX-M) as well as both virulence marker genes (pai and hly) were detected in above 90% of E. coli. Conclusion: the data illustrate an alarming increase in UPEC with ESBL production and the emergence of multidrug-resistant drugs in the early age of children. The public health sectors should further monitor the guidelines of using antibiotics in Kurdistan, Iraq.

Recent advances in β-lactamase inhibitor chemotypes and inhibition modes

The effectiveness of β-lactam antibiotics is increasingly influenced by serine β-lactamases (SBLs) and metallo-β-lactamases (MBLs), which can hydrolyze β-lactam antibiotics. The development of effective β-lactamase inhibitors is an important direction to extend use of β-lactam antibiotics. Although six SBL inhibitors have been approved for clinical use, but no MBL inhibitors or MBL/SBL dual-action inhibitors are available so far. Broad-spectrum targeting clinically relevant MBLs and SBLs is currently desirable, while it is not easy to achieve such a purpose owing to structural and mechanistic differences between MBLs and SBLs. In this review, we summarized recent advances of inhibitor chemotypes targeting MBLs and SBLs and their inhibition mechanisms, particularly including lead discovery and structural optimization strategies, with the aim to provide useful information for future efforts to develop new MBL and SBL inhibitors.

Optimizing Doses of Ceftolozane/Tazobactam as Monotherapy or in Combination with Amikacin to Treat Carbapenem-Resistant Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a hospital-acquired pathogen with a high mortality rate and limited treatment options. We investigated the activity of ceftolozane/tazobactam (C/T) and its synergistic effects with amikacin to extend the range of optimal therapeutic choices with appropriate doses. The E-test method is used to determine in vitro activity. The optimal dosing regimens to achieve a probability of target attainment (PTA) and a cumulative fraction of response (CFR) of ≥90% were simulated using the Monte Carlo method. Of the 66 CRPA isolates, the rate of susceptibility to C/T was 86.36%, with an MIC50 and an MIC90 of 0.75 and 24 µg/mL, respectively. Synergistic and additive effects between C/T and amikacin were observed in 24 (40%) and 18 (30%) of 60 CRPA isolates, respectively. The extended infusion of C/T regimens achieved a ≥90% PTA of 75% and a 100% fT > MIC at C/T MICs of 4 and 2 µg/mL, respectively. Only the combination of either a short or prolonged C/T infusion with a loading dose of amikacin of 20−25 mg/kg, followed by 15−20 mg/kg/day amikacin dosage, achieved ≥90% CFR. The C/T infusion, combined with currently recommended amikacin dose regimens, should be considered to manage CRPA infections.

N-Aryl Mercaptopropionamides as Broad-Spectrum Inhibitors of Metallo-β-Lactamases

Drug-resistant pathogens pose a global challenge to public health as they cause diseases that are extremely difficult to cure. Metallo-β-lactamases (MBLs) are a diverse set of zinc-containing enzymes that catalyze the hydrolysis of β-lactam drugs, including carbapenems, which are considered as the last resort to fight severe infections. To restore the activity of current β-lactam antibiotics and to offer an orthogonal strategy to the discovery of new antibiotics, we have identified a series of polar N-aryl mercaptopropionamide derivatives as potent inhibitors of several class B1 MBLs. We have identified a hit structure with high selectivity restoring the effect of imipenem and reducing minimum inhibitory concentration (MIC) values up to 256-fold in resistant isolates from Escherichia coli. Furthermore, the combination of imipenem with our inhibitor showed in vivo efficacy in a Galleria mellonella model, increasing the survival rate of infected larvae by up to 31%.

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

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

Glutamine promotes antibiotic uptake to kill multidrug-resistant uropathogenic bacteria

[Figure: see text].

Amino Acid Based Antimicrobial Agents - Synthesis and Properties

Structures of several dozen of known antibacterial, antifungal or antiprotozoal agents are based on the amino acid scaffold. In most of them, the amino acid skeleton is of a crucial importance for their antimicrobial activity, since very often they are structural analogs of amino acid intermediates of different microbial biosynthetic pathways. Particularly, some aminophosphonate or aminoboronate analogs of protein amino acids are effective enzyme inhibitors, as structural mimics of tetrahedral transition state intermediates. Synthesis of amino acid antimicrobials is a particular challenge, especially in terms of the need for enantioselective methods, including the asymmetric synthesis. All these issues are addressed in this review, summing up the current state‐of‐the‐art and presenting perspectives fur further progress.

Role of new antibiotics in extended-spectrum β-lactamase-, AmpC- infections

PURPOSE OF REVIEW

Extended-spectrum β-lactamases (ESBL)- and ampicillinase class C (AmpC)-producing Enterobacterales represent one of the major public threats of the current era. As a consequence, during the last decades there have been great efforts to develop new therapeutic agents against these microorganisms. The aim of this review is to summarize the clinical features associated with novel antibiotics with activity against ESBL- and AmpC-producing isolates.

RECENT FINDINGS

There a number of therapeutic agents with activity against ESBL and AmpC than have been introduced and approved over the past few years. Ceftazidime-avibactam and ceftolozane-tazobactam are both carbapenem sparing agents that appear interesting alternatives for treatment of serious Gram-negative infections. Other new β-lactams/ β-lactamase inhibitors (e.g. cefepime-enmetazobactam; ceftaroline fosamil-avibactam; aztreonam-avibactam and cefepime-zidebactam) as well as eravacycline, omadacycline, and plazomicin are also promising agents for treatment of ESBL- and AmpC- infections, but further clinical data are needed to establish their efficacy in comparison to carbapenems. The role of carbapenems/ β-lactamase inhibitors remains to be clarified.

SUMMARY

New therapeutic agents against ESBL- and AmpC-producing Enterobacterales have distinctive specificities and limitations that require further investigations. Future randomized clinical trials are required to define the best strategy for their use in patients with serious infections due to ESBL- and/or AmpC- infections.

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.

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.

Study of the Antimicrobial Potential of Bacteria found in Natural Resources

Bacteriocins are of great interest as potential antimicrobial agents against various types of bacteria, fungi, and viruses. Isolates of microorganisms derived from natural sources were used in the current study, including lactic acid bacteria and other antagonistic microorganisms. The species of the microorganisms were determined using 16S rDNA and ITS nrDNA analyses. E. coli, S. enterica, S. aureus, P. aeruginosa, B. mycoides, A. faecalis, P. vulgaris, S. flexneri , L. monocytogenes, C. albicans, A. flavus, and P. citrinum were used as pathogenic and opportunistic strains. It was found that 11 strains of antagonistic microorganisms have significant antimicrobial activity against all pathogenic and opportunistic microorganisms. The antimicrobial properties of these microorganisms are currently under study.

Antimicrobial Resistance Conferred by OXA-48 β-Lactamases: Towards a Detailed Mechanistic Understanding

OXA-48-type β-lactamases are now routinely encountered in bacterial infections caused by carbapenem-resistant Enterobacterales These enzymes are of high and growing clinical significance due to the importance of carbapenems in treatment of health care-associated infections by Gram-negative bacteria, the wide and increasing dissemination of OXA-48 enzymes on plasmids, and the challenges posed by their detection. OXA-48 confers resistance to penicillin (which is efficiently hydrolyzed) and carbapenem antibiotics (which is more slowly broken down). In addition to the parent enzyme, a growing array of variants of OXA-48 is now emerging. The spectrum of activity of these variants varies, with some hydrolyzing expanded-spectrum oxyimino-cephalosporins. The growth in importance and diversity of the OXA-48 group has motivated increasing numbers of studies that aim to elucidate the relationship between structure and specificity and establish the mechanistic basis for β-lactam turnover in this enzyme family. In this review, we collate recently published structural, kinetic, and mechanistic information on the interactions between clinically relevant β-lactam antibiotics and inhibitors and OXA-48 β-lactamases. Collectively, these studies are starting to form a detailed picture of the underlying bases for the differences in β-lactam specificity between OXA-48 variants and the consequent differences in resistance phenotype. We focus specifically on aspects of carbapenemase and cephalosporinase activities of OXA-48 β-lactamases and discuss β-lactamase inhibitor development in this context. Throughout the review, we also outline key open research questions for future investigation.

Epidemiology of Meropenem/Vaborbactam Resistance in KPC-Producing Klebsiella pneumoniae Causing Bloodstream Infections in Northern Italy, 2018

Meropenem/Vaborbactam (MEM-VAB) is a novel carbapenem- β-lactamase inhibitor active against KPC-producing Enterobacteria. Herein, we evaluate the incidence of meropenem/vaborbactam-resistance among KPC-producing K. pneumoniae (KPC-Kp) bloodstream infection in a large Italian hospital. Meropenem/vaborbactam-resistance was found in 8% (n = 5) KPC-Kp, while 5% (n = 3) strains exhibited cross-resistance to ceftazidime/avibactam (CAZ-AVI). Genomic analysis revealed that meropenem/vaborbactam-resistance was associated with truncated OmpK35 and insertion of glycine and aspartic acid within OmpK36 at position 134–135 (GD134–135). Notably, no specific mutation was associated to cross-resistance. No specific antimicrobial treatment was related to favorable clinical outcomes, while cross-resistance was not associated to higher clinical and/or microbiological failures. Our study indicated that resistance to meropenem/vaborbactam was due to porins mutations and is associated with reduced susceptibility to both ceftazidime/avibactam and carbapenems.

Clinical Outcomes in Carbapenem-Resistant Enterobacteriaceae Infections Treated With Ceftazidime-Avibactam: A Single-Center Observational Study

Introduction Among the several newer beta lactam+beta lactase inhibitors (BL/BLI), ceftazidime-avibactam is the only drug showing activity against OXA-48-like producers. Hence, it is being increasingly used in India to treat infections caused by carbapenem-resistant Enterobacteriaceae (CRE), especially as a colistin-sparing agent. We have used ceftazidime-avibactam in patients suspected and confirmed to have CRE infections in our center, and present a retrospective analysis of our experience. Methods We conducted a single-center, retrospective study involving all patients who were treated with ceftazidime-avibactam for suspected and proven CRE infections during a one-year period at our 500-bedded hospital. Our primary objective for this study was taken as all-cause mortality. The secondary objectives were to determine the clinical cure, defined as the end of the treatment regimen with a resolution of primary infection and resistance to ceftazidime-avibactam in patients who underwent the Epsilometer test (E-test). Results  A total of 103 patients who received ceftazidime-avibactam were identified. The all-cause mortality was 27% while a clinical cure was achieved in 73%. Fifty-two patients received empirical therapy and 51 patients received ceftazidime-avibactam for confirmed CRE infection. Forty-eight patients had an E-test done, out of which 79% of patients had CREs sensitive to ceftazidime-avibactam, and 21% of patients had ceftazidime-avibactam resistant CREs. A higher Sequential Organ Failure Assessment (SOFA) score, Charlson comorbidity index (CCI) score, intensive care unit (ICU) admission, inotrope requirement, and lower days of therapy (DOT) with ceftazidime-avibactam were found to be associated with increased mortality. Conclusion Colistin has been considered to be the last-line agent in CRE infections, but there are concerns about its adverse effects and the emergence of resistance. Given our relatively low mortality of 27% in CRE infections treated with ceftazidime-avibactam, coupled with the high susceptibility of the tested isolates, there may be a role for the empirical use of this drug in infections caused by CRE, especially in a setting where colistin may not be ideal.

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.

β-lactamase inhibitory potential of kalafungin from marine Streptomyces in Staphylococcus aureus infected zebrafish

β-lactamase inhibitors are potent synergistic drugs to deteriorate the multidrug-resistant bacteria. Here, we report the β-lactamase inhibitory ability of kalafungin isolated from a marine sponge derived Streptomyces sp. SBRK1. The IC₅₀ value of the kalafungin was calculated as 225.37 ± 1.95 μM against β-lactamase. The enzyme kinetic analysis showed the Km value of 3.448 ± 0.7 μM and V_max value of 215.356 ± 8 μM/min and the inhibition mechanism was identified as uncompetitive type. Along with the antibacterial activity, the cell surface analysis of kalafungin treated Staphylococcus aureus cells revealed destruction of cell membrane in response to β-lactamase inhibition. Molecular docking studies have confirmed the binding property of kalafungin against β-lactamase with two hydrogen bonds. In vivo efficacy studies in the zebrafish model by green fluorescent protein expressing S. aureus infection, survival, safety and behavioral profile were reported. The toxicity and anti-infection revealed that the compound was evidently active and safe to all organs. In conclusion, this is the first report on kalafungin with β- lactamase inhibition and suggests that kalafungin may useful for synergic antibacterial therapy with β-lactam drugs to overcome β-lactamase-based resistance of any bacterial pathogens.

Treatment of extended-spectrum β-lactamases infections: what is the current role of new β-lactams/β-lactamase inhibitors?

PURPOSE OF REVIEW

The widespread diffusion of extended-spectrum β-lactamases (ESBLs)-producing Enterobacteriales currently represents a major threat for public health worldwide. Carbapenems are currently considered the first-line choice for serious ESBL infections. However, the dramatic global increase in ESBL prevalence has led to a significant overuse of carbapenems that has promoted the selection and spread of carbapenemases, which might further prejudicated our ability to treat infections due to multidrug-resistant pathogens. Therefore, strategies to limit the use of carbapenems should be implemented.

RECENT FINDINGS

Although piperacillin-tazobactam should no longer be considered an alternative to carbapenems for definitive treatment of bloodstream infections due to ESBL-producing strains, it might still represent an alternative for step-down therapy or for low-to-moderate severity infection originating from urinary or biliary sources and when piperacillin-tazobactam minimum inhibitory concentration of 4 mg/l or less. Ceftazidime-avibactam and ceftolozane-tazobactam are both carbapenem sparing agents that appear interesting alternatives for treatment of serious ESBL infections. New β-lactams/β-lactamase inhibitors (BL/BLI), including cefepime-enmetazobactam, ceftaroline fosamil-avibactam, aztreonam-avibactam and cefepime-zidebactam, are also promising agents for treatment of ESBL infections, but further clinical data are needed to establish their efficacy relative to carbapenems. The role of carbapenems/β-lactamase inhibitors remain to be clarified.

SUMMARY

New BL/BLI have distinctive specificities and limitations that require further investigations. Future randomized clinical trials are required to define the best strategy for their administering for ESBL infections.

Imipenem-Relebactam Susceptibility Testing of Gram-Negative Bacilli by Agar Dilution, Disk Diffusion, and Gradient Strip Methods Compared with Broth Microdilution

This study aimed to determine whether agar dilution, research-use-only disk diffusion (Mast Group Ltd., Bootle Merseyside, UK), Etest (bioMérieux, Inc., Durham, NC), and MIC test strip (MTS) (Liofilchem, Inc., Waltham, MA) methods yield equivalent results to those of broth microdilution (BMD) for imipenem-relebactam susceptibility testing using a collection of 297 Gram-negative bacilli, including members of the order Enterobacterales and Pseudomonas aeruginosa, enriched for drug resistance. MIC and disk diameter results were interpreted using United States Food and Drug Administration breakpoints. Overall, 76.8% of the isolates tested were susceptible to imipenem-relebactam by BMD. MIC values for agar dilution, Etest, and MTS were not significantly different from that for BMD, although they tended to be 1 to 2 dilutions higher. Essential agreement was 95.6% for agar dilution, 90.6% for Etest, and 85.2% for MTS. Categorical agreement was 98.0% for agar dilution, 73.1% for disk diffusion, 96.3% for Etest, and 96.6% for MTS. In conclusion, agar dilution and Etest yielded comparable results to BMD for imipenem-relebactam.

The role of new β-lactamase inhibitors in gram-negative infections

PURPOSE OF REVIEW

In recent years, traditional β-lactams have dramatically reduced their effectiveness against gram-negative bacteria mainly because of their ability to express multiple β-lactamase or carabapenemases that are not hydrolyzed by the old β-lactam inhibitors (BLIs) such as clavulanic acid, tazobactam, and sulbactam. New BLIs molecules have been developed to face the need of compounds that are active against multidrug or pandrug resistant gram-negative pathogens. The aim of this review is to summarize the new generation of BLIs and β-lactams combinations.

RECENT FINDINGS

A number of new molecules with activity against Ambler class A (e.g., extended-spectrum β-lactamases, serine carbapenemases), class C (e.g., AmpC), or class D (e.g., oxacillinase-48) have been recently approved in combination with old β-lactams for the treatment of multidrug-resistant bacteria, and other agents are under investigation. These new compounds include diazabicyclooctanones non-β-lactam inhibitors (e.g., avibactam, relebactam, nacubactam) and boronic acid inhibitors (e.g., vaborbactam).

SUMMARY

Newly approved and investigational new BLIs are expected to offer many advantages for the management of patients with multidrug-resistant gram-negative pathogens. Promising characteristics of new compounds include high activity against multi drug resistance gram-negative bacteria and a favorable safety profile.

Structural studies of triazole inhibitors with promising inhibitor effects against antibiotic resistance metallo-β-lactamases

Metallo-β-lactamases (MBLs) are an emerging cause of bacterial antibiotic resistance by hydrolysing all classes of β-lactams except monobactams, and the MBLs are not inhibited by clinically available serine-β-lactamase inhibitors. Two of the most commonly encountered MBLs in clinical isolates worldwide - the New Delhi metallo-β-lactamase (NDM-1) and the Verona integron-encoded metallo-β-lactamase (VIM-2) - are included in this study. A series of several NH-1,2,3-triazoles was prepared by a three-step protocol utilizing Banert cascade reaction as the key step. The inhibitor properties were evaluated in biochemical assays against the MBLs VIM-2, NDM-1 and GIM-1, and VIM-2 showed IC₅₀ values down to nanomolar range. High-resolution crystal structures of four inhibitors in complex with VIM-2 revealed hydrogen bonds from the triazole inhibitors to Arg228 and to the backbone of Ala231 or Asn233, along with hydrophobic interactions to Trp87, Phe61 and Tyr67. The inhibitors show reduced MIC in synergy assays with Pseudomonas aeruginosa and Escherichia coli strains harbouring VIM enzymes. The obtained results will be useful for further structural guided design of MBL inhibitors.

Bacteriocins, Antimicrobial Peptides from Bacterial Origin: Overview of Their Biology and Their Impact against Multidrug-Resistant Bacteria

Currently, the emergence and ongoing dissemination of antimicrobial resistance among bacteria are critical health and economic issue, leading to increased rates of morbidity and mortality related to bacterial infections. Research and development for new antimicrobial agents is currently needed to overcome this problem. Among the different approaches studied, bacteriocins seem to be a promising possibility. These molecules are peptides naturally synthesized by ribosomes, produced by both Gram-positive bacteria (GPB) and Gram-negative bacteria (GNB), which will allow these bacteriocin producers to survive in highly competitive polymicrobial environment. Bacteriocins exhibit antimicrobial activity with variable spectrum depending on the peptide, which may target several bacteria. Already used in some areas such as agro-food, bacteriocins may be considered as interesting candidates for further development as antimicrobial agents used in health contexts, particularly considering the issue of antimicrobial resistance. The aim of this review is to present an updated global report on the biology of bacteriocins produced by GPB and GNB, as well as their antibacterial activity against relevant bacterial pathogens, and especially against multidrug-resistant bacteria.

Photodynamic inactivation of bacterial carbapenemases restores bacterial carbapenem susceptibility and enhances carbapenem antibiotic effectiveness

The global emergence of carbapenemases in bacterial pathogens has rendered many life-threatening infections untreatable. Even though using carbapenemase inhibitors are a proven strategy in the battle against bacterial carbapenem resistance, developing inhibitors that could universally inactivate all bacterial carbapenemases is extremely challenging given the large diversity and the continuous evolution of bacterial carbapenemases. Antimicrobial photodynamic therapy (aPDT), an upcoming antimicrobial therapy, is demonstrated here for the first time to be a generalized approach to impair the bacterial carbapenemases without being limited by the molecular identities of the carbapenemases. In addition, aPDT is shown to prevent carbapenem antibiotic degradation, thereby enhancing the efficacy of carbapenem antibiotic against the carbapenemase-producing pathogens. Besides the enzyme activity impairment, aPDT was documented here to be genetically toxic for bacteria, and thus radically damage the carbapenemase genetic determinants in bacteria and prevent the transmission of carbapenemases among pathogens. By leveraging the universal carbapenemase-inactivating property of aPDT, it may be possible to make the incurable infections caused by the bacterial carbapenemases susceptible to carbapenem again.

Experience With Ceftolozane-Tazobactam for the Treatment of Serious Pseudomonas aeruginosa Infections in Saudi Tertiary Care Center

Introduction:

Multidrug-resistant Pseudomonas aeruginosa isolates have multiple resistance mechanisms, and there are insufficient therapeutic options to target them. Ceftolozane-tazobactam is a novel antipseudomonal agent that contains a combination of an oxyimino-aminothiazolyl cephalosporin (ceftolozane) and a β-lactamase inhibitor (tazobactam).

Methods:

A single-center retrospective observational study between January 2017 and December 2018 for patients who had been diagnosed with carbapenem-resistant P aeruginosa infections and treated with ceftolozane-tazobactam for more than 72 hours. We assessed clinical success based on microbiological clearance as well as the clinical resolution of signs and symptoms of infection.

Results:

A total of 19 patients fit the inclusion criteria, with a median age was 57 years, and 53% were female. The types of infections were nosocomial pneumonia, acute bacterial skin, and skin structure infections; complicated intra-abdominal infections; and central line–associated bloodstream infections. All of the isolates were resistant to both meropenem and imipenem. The duration of therapy was variable (average of 14 days). At day 14 of starting ceftolozane-tazobactam, 18 of 19 patients had a resolution of signs and symptoms of the infection. Only 14 of 19 patients (74%) had proven microbiological eradication observed at the end of therapy. During therapy, there was no adverse event secondary to ceftolozane-tazobactam, and no Clostridium difficile infection was identified. The 30-day mortality rate was 21% (4/19).

Conclusions:

Multidrug-resistant P aeruginosa infection is associated with high mortality, which would potentially be improved using a new antibiotic such as ceftolozane-tazobactam. Studies are required to explain the role of combination therapy, define adequate dosing, and identify the proper duration of treatment.

Ceftolozane/Tazobactam Dosing Requirements Against Pseudomonas aeruginosa Bacteremia

Objectives

To assess the probability of reaching adequate pharmacokinetic/pharmacodynamics values for ceftolozane/tazobactam at different doses and degrees of renal functions in patients with Pseudomonas aeruginosa bacteremia.

Methods

Six dosing regimens were evaluated: 0.5/0.25 g, 1/0.5 g, and 2/1 g every 8 hours given as 1 hour or 3 hours infusions. Pharmacokinetic data were obtained from the literature. Susceptibility data to ceftolozane were collected from patients with P aeruginosa infection treated with ceftolozane-tazobactam. Probability of reaching a fraction of time (fT) >40% minimum inhibitory concentration (MIC) and fT >100%MIC value for ceftolozane at 3 different renal clearance values was evaluated. For tazobactam, the probability of reaching an fT >40% and >70% for 3 limit values was calculated.

Results

Thirty-seven strains were included. For ceftolozane, the probability of reaching a fT >40%MIC was greater than 90% for any degree of renal function. The probability of reaching a fT >100%MIC for 1 g dose infused over 1 hour and 3 hours was 82.2% and 86.4% for a creatinine clearance (ClCr) >90 mL/min. Using a 2 g dose, the probability was greater than 90% for both infusions rates. For tazobactam, the probability of reaching a value of fT >50% of the limit concentrations was greater than 90% for a ClCr of 70 mL/min. In the case of a ClCr >90 mL/min and limit concentration values ≥ 0.25 mg/mL, only extended infusions showed a probability >90%.

Conclusions and Relevance

The standard doses of ceftolozane/tazobactam achieve an adequate fT >40%MIC value. However, doses of 2 g in extended infusion is necessary to reach a value of fT >100%MIC, especially in patients with an increased renal clearance and high levels of beta-lactamases expression.

A review on bacterial resistance to carbapenems: epidemiology, detection and treatment options

Carbapenems are a class of antimicrobial agents reserved for infections caused by multidrug-resistant microorganisms. The emergence of carbapenem resistance has become a serious public health threat. This type of antimicrobial resistance is spreading at an alarming rate, resulting in major outbreaks and treatment failure of community-acquired and nosocomial infections caused by the clinically relevant carbapenem-producing Enterobacteriaceae or carbapenem-resistant Enterobacteriaceae. This review is focused on carbapenem resistance, including mechanisms of resistance, history and epidemiology, phenotypic and genotypic detection in the clinically relevant bacterial pathogens and the possible treatment options available.

Carbapenemase-producing Enterobacteriaceae - once positive always positive?

PURPOSE OF REVIEW

This review provides an overview of gastrointestinal tract colonization with carbapenemase-producing Enterobacteriaceae (CPE), including risk factors for colonization, determinants for duration of colonization, and whether patients can decolonize, either spontaneously or via targeted interventions.

RECENT FINDINGS

CPE colonization is disseminating globally with increasing numbers of carbapenemases being identified in increasing patient cohorts. Numerous risk factors including repeated healthcare contact, patient co-morbidities and international travel have all been linked to increased rates of colonization. Duration of colonization has been investigated in various healthcare settings and ranges many months or even years. Although new methods for expediting decolonization are being investigated, including faecal microbiota transplantation, high quality evidence of impact is lacking.

SUMMARY

Current evidence indicates that CPE colonization usually persists throughout the duration of most hospital admissions, although the majority of patients will subsequently spontaneously decolonize. Difficulties remain in determining the point at which patients can be considered decolonized because of the lack acceptable criteria for defining eradication. This has significance implications for infection prevention and control measures during the initial and subsequent hospital admissions. Strategies to reduce the healthcare burden of CPE colonization continue to rely predominantly on preventing acquisition, whereas decolonization efforts remain a focus of research.

Discovery of mercaptopropanamide-substituted aryl tetrazoles as new broad-spectrum metallo-β-lactamase inhibitors

β-Lactam antibiotic resistance mediated by metallo-β-lactamases (MBL) has threatened global public health. There are currently no available inhibitors of MBLs for clinical use. We previously reported the ruthenium-catalyzed meta-selective C–H nitration synthesis method, leading to some meta-mercaptopropanamide substituted aryl tetrazoles as new potent MBL inhibitors. Here, we described the structure–activity relationship of meta- and ortho-mercaptopropanamide substituted aryl tetrazoles with clinically relevant MBLs. The resulting most potent compound 13a showed IC₅₀ values of 0.044 μM, 0.396 μM and 0.71 μM against VIM-2, NDM-1 and IMP-1 MBL, respectively. Crystallographic analysis revealed that 13a chelated to active site zinc ions via the thiol group and interacted with the catalytically important residues Asn233 and Tyr67, providing further structural information for the development of thiol based MBL inhibitors.

Compound 13a showed IC₅₀ values of 0.044 μM, 0.396 μM and 0.71 μM against VIM-2, NDM-1 and IMP-1 MBL, respectively. It binds to chelates via active site zinc ions and forms interactions with residues on the L1 and L3 loops of VIM-2.

Use of Ceftolozane-Tazobactam in Patient with Severe Medium Chronic Purulent Otitis by XDR Pseudomonas aeruginosa

We present a case of a male Italian patient of 66 years with a history of kidney transplantation in treatment with cyclosporine and methylprednisolone. He visited an ENT clinic and was diagnosed as chronic left purulent otitis media. He began at-home antibiotic therapy with poor benefit. On 09/13/18, he was admitted to the hospital "S. Maria "of Terni for persistence of left ear pain and complete hearing loss. Magnetic resonance imaging (MRI) of the brain showed "in correspondence of the petrous rock and the mastoid…presence of flogistic tissue." Auricular swabs and later surgical drainage of the purulent material were performed and both were positive for extensively drug-resistant (XDR) Pseudomonas aeruginosa sensitive only to colistin in absence of synergism with rifampin. The patient underwent antibiotic therapy with ceftolozane-tazobactam, a new generation cephalosporin with anti-Pseudomonas activity and a β-lactamase inhibitor, that currently is indicated for the treatment of complicated urinary tract infections and complicated intra-abdominal infections, with complete healing. In literature, it is described a series of 12 patients with severe MDR (multidrug-resistant) Pseudomonas aeruginosa infections (6 pneumonia) who received salvage therapy with ceftolozane-tazobactam after inappropriate empirical and/or suboptimal treatment. This study included a case of a male patient of 45 years, affected by Burkitt lymphoma and severe neutropenia, who presented with otitis and mastoiditis, and isolation of Pseudomonas aeruginosa in surgical drainage of the purulent material of the ear (blood cultures were negative). He underwent antibiotic therapy with ceftolozane-tazobactam at a dosage of 3 g/8 h for 21.3 days. The patient was healed, but a late recurrence was described because of isolation of ceftolozane-tazobactam-resistant Pseudomonas after therapy. The possibility of acquiring resistance to ceftolozane-tazobactam should be considered in patients with previous exposure to beta-lactams and with poor response to these antibiotics.

In vitro activity of meropenem combined with vaborbactam against KPC-producing Enterobacteriaceae in China

Background

Vaborbactam is a novel inhibitor of serine β-lactamases, including KPCs, which predominate in China. It is being developed in combination with meropenem.

Methods

Using the broth microdilution method, the in vitro activity of meropenem/vaborbactam against 128 KPC-producing Enterobacteriaceae from China was investigated.

Results

Meropenem alone showed no activity (MIC50 and MIC90 >64 mg/L), but the addition of vaborbactam potentiated meropenem in a dose-dependent manner with MIC90 decreasing from >64 to 0.5 mg/L in the presence of increasing concentrations of vaborbactam. MIC50 and MIC90 of meropenem with 8 mg/L vaborbactam (MV8) were reduced to 0.5 and 8 mg/L, respectively. MV8 (4 mg/L meropenem) inhibited 76.6% of Klebsiella pneumoniae and 100% of Escherichia coli isolates. Seventy-three (77.7%) of the K. pneumoniae isolates belonged to ST11; the remaining 22.3% of isolates were represented by 12 different STs. Of the ST11 and non-ST11 isolates, 71.2% and 95.2%, respectively, were inhibited by MV8 (4 mg/L meropenem). In 14 strains characterized for intrinsic resistance mechanisms, MV8 MIC was increased in isolates with defects in both OmpK35 and OmpK36. The highest MV8 MIC was observed in the strain that had both non-functional porins and increased expression of blaKPC and acrB.

Conclusions

Our findings suggest that meropenem/vaborbactam has good activity against KPC-producing Enterobacteriaceae from China. However, a higher percentage of K. pneumoniae isolates for which MV8 MIC was elevated compared with other geographical areas is noteworthy. This might be due to clonal dissemination of ST11 KPC-producing isolates that are defective in both major porins, OmpK35 and OmpK36.

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.

Both the mono- and di-anions of ellagic acid are effective inhibitors of the serine β-lactamase CTX-M-15

Ellagic acid, a δ-lactone with ionisable phenolic residues, is an efficient time-dependent inhibitor of the serine β-lactamase enzyme CTX-M-15. The pH-dependence of the rate of inhibition shows that both the mono- and di-anionic species of ellagic acid are effective inhibitors, both with second order rate constants of ∼1.5 × 10⁴ M^-1 s^-1. The structurally similar δ-lactone urolithin A, which lacks the geometrically appropriate phenolic residue, shows only modest inhibitory activity against CTX-M-15. It is proposed that this inhibition by ellagic acid anions involves acylation of the active site serine and that the negative charge on the inhibitor is required for binding to the active site.

Carbapenem-Resistant Enterobacteriaceae Posing a Dilemma in Effective Healthcare Delivery

The emergence and spread of Carbapenem-resistant Enterobacteriaceae (CRE) is seriously posing threats in effective healthcare delivery. The aim of this study was to ascertain the emergence of CRE at Chukwuemeka Odumegwu Ojukwu University Teaching Hospital (COOUTH) Awka. Biological samples were collected from 153 consenting patient from 5 clinics in the hospital. The isolates were identified using standard microbiological protocols. Susceptibility to meropenem was done using Kirby-Bauer disc diffusion method on Mueller Hinton Agar. A total of 153 patients were recruited in this study. About one half of those from rural, 63.64% from Sub-urban and 42.27% from urban areas had significant E. coli and Klebsiella spp infections. The male: female ratio of the Enterobacteriaceae infection was 1:1. Almost as much inpatient as outpatient study participants had the infections. The infections were observed mostly on participants with lower educational status. The unmarried individuals were most infected compared to their married counterparts. Enterobacteriaceae infection rate was 50.98%. Of this, 28.21% had CRE infection while the overall prevalence of the CRE in the studied population was 14.38% (22/153). This study shows that CRE is quickly emerging in both community and hospital environments. Klebsiella spp was the most common CRE in this hospital especially Klebsiella oxytoca. Hospitalization was a strong risk factor in the CRE infections. Rapid and accurate detection is critical for their effective management and control.

Active-Site Druggability of Carbapenemases and Broad-Spectrum Inhibitor Discovery

Serine and metallo-carbapenemases are a serious health concern due to their capability to hydrolyze nearly all β-lactam antibiotics. However, the molecular basis for their unique broad-spectrum substrate profile is poorly understood, particularly for serine carbapenemases, such as KPC-2. Using substrates and newly identified small molecules, we compared the ligand binding properties of KPC-2 with the noncarbapenemase CTX-M-14, both of which are Class A β-lactamases with highly similar active sites. Notably, compared to CTX-M-14, KPC-2 was more potently inhibited by hydrolyzed β-lactam products (product inhibition), as well as by a series of novel tetrazole-based inhibitors selected from molecular docking against CTX-M-14. Together with complex crystal structures, these data suggest that the KPC-2 active site has an enhanced ability to form favorable interactions with substrates and small molecule ligands due to its increased hydrophobicity and flexibility. Such properties are even more pronounced in metallo-carbapenemases, such as NDM-1, which was also inhibited by some of the novel tetrazole compounds, including one displaying comparable low μM affinities against both KPC-2 and NDM-1. Our results suggest that carbapenemase activity confers an evolutionary advantage on producers via a broad β-lactam substrate scope but also a mechanistic Achilles' heel that can be exploited for new inhibitor discovery. The complex structures demonstrate, for the first time, how noncovalent inhibitors can be engineered to simultaneously target both serine and metallo-carbapenemases. Despite the relatively modest activity of the current compounds, these studies also demonstrate that hydrolyzed products and tetrazole-based chemotypes can provide valuable starting points for broad-spectrum inhibitor discovery against carbapenemases.

Antimicrobial treatment challenges in the era of carbapenem resistance

Infections due to carbapenem-resistant Gram-negative bacteria are burdened by high mortality and represent an urgent threat to address. Clinicians are currently at a dawn of a new era in which antibiotic resistance in Gram-negative bacilli is being dealt with by the availability of the first new antibiotics in this field for many years. Although new antibiotics have shown promising results in clinical trials, there is still uncertainty over whether their use will improve clinical outcomes in real world practice. Some observational studies have reported a survival benefit in carbapenem-resistant Enterobacteriaceae bloodstream infections using combination therapy, often including "old" antibiotics such as colistin, aminoglycosides, tigecycline, and carbapenems. These regimens, however, are linked to increased risk of antimicrobial resistance, and their efficacy has yet to be compared to new antimicrobial options. While awaiting more definitive evidence, antibiotic stewards need clear direction on how to optimize the use of old and novel antibiotic options. Furthermore, carbapenem-sparing regimens should be carefully considered as a potential tool to reduce selective antimicrobial pressure.

Epidemiology of carbapenemase-producing Enterobacteriaceae in a pediatric hospital in a country with high endemicity

BACKGROUND

Little is known about epidemiology of carbapenemase-producing Enterobacteriaceae (CPE) in children. Aim of this study was to describe CPE epidemiology in a tertiary care pediatric hospital in Italy that admits patients coming from geographic areas with high diffusion of CPE.

METHODS

Prospective evaluation of the proportion and rates per 100,000 hospital discharges (D) or hospitalization-days (HD) of invasive infections due to CPE from 2013 to 2017 and of CPE infections and colonizations from 2014 to 2017. Disease-preventing strategies comprised patients' screening at admission, pre-emptive contact isolation precautions pending cultures results, and bundles for prevention of healthcare associated infections.

RESULTS

From 2013 to 2017 CPE represented 3.5% of all invasive infections due to Enterobacteriaceae, with rates ranging 7.30-14.33 for D and 1.03-2.06 for HD, without major changes over time. On the contrary, overall rates of isolates increased from 83.03 to 191.34 for D and from 12.21 to 28.35 for HD. The intra-hospital diffusion consisted of 2 small outbreaks without invasive diseases in 2014-2015, and sporadic, not epidemiologically-related cases in 2016-2017. Globally, Escherichia coli and Klebsiella pneumoniae represented 64% of identified CPE, while 70% of carbapenemases identified were metallo-beta-lactamases (VIM or NDM), with changes over time.

CONCLUSIONS

In our center metallo-beta lactamases were the most frequently identified carbapenemases in Enterobacteriaceae and E. coli and K. pneumoniae the most frequently isolated pathogens carrying these enzymes. A proactive management strategy was effective in containing in-hospital spreading.

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.

Orally Absorbed Derivatives of the β-Lactamase Inhibitor Avibactam. Design of Novel Prodrugs of Sulfate Containing Drugs

Only one FDA-approved β-lactamase inhibitor has ever been orally available: clavulanic acid, approved in 1984. Avibactam, approved by FDA in 2015, is the first of a new class of BLIs called diazabicyclooctanes, or "DBOs". This class has much broader coverage than clavulanic acid but can only be administered by intravenous injection. Herein, we describe the synthesis and testing of the first approved BLI to be rendered orally bioavailable since clavulanic acid (1984).