As a bacterial resistance strategy, serine beta-lactamases have evolved from cell wall synthesizing enzymes known as penicillin-binding proteins (PBP), by not only covalently binding beta-lactam antibiotics but, also acquiring mechanisms of deacylating these antibiotics. This critical deacylation step leads to release of hydrolyzed and inactivated beta-lactams, thereby providing resistance for the bacteria against these antibiotics targeting the cell wall. To combat beta-lactamase-mediated antibiotic resistance, numerous beta-lactamase inhibitors were developed that utilize various strategies to inactivate the beta-lactamase. Most of these compounds are "mechanism-based" inhibitors that in some manner mimic the beta-lactam substrate, having a carbonyl moiety and a negatively charged carboxyl or sulfate group. These compounds form a covalent adduct with the catalytic serine via an initial acylation step. To increase the life-time of the inhibitory covalent adduct intermediates, a remarkable array of different strategies was employed to improve inhibition potency. Such approaches include post-acylation intra- and intermolecular chemical rearrangements as well as affecting the deacylation water. These approaches transform the inhibitor design process from a 3-dimensional problem (i.e., XYZ coordinates) to one with additional dimensions of complexity as the reaction coordinate and time spent at each chemical state need to be taken into consideration. This review highlights the mechanistic intricacies of the design efforts of the beta-lactamase inhibitors which so far have resulted in the development of "two generations" and 5 clinically available inhibitors.

Whole-genome sequencing (WGS) using MinION was used to characterize high-risk clones of Escherichia coli and Klebsiella pneumoniae harboring bla(NDM-5), bla(OXA-181), and bla(CTX-M-15), as well as Pseudomonas aeruginosa harboring bla(NDM), in a patient who received health care in India. Synergy testing demonstrated the activity of aztreonam and ceftazime-avibactam in combination. This case illustrates a "precision medicine" approach where deeper understanding of the genotype through WGS and of the phenotype through synergy testing formed the basis for rational combination therapy.

Understanding the nuances of AmpC beta-lactamase-mediated resistance can be challenging, even for the infectious diseases specialist. AmpC resistance can be classified into 3 categories: (1) inducible chromosomal resistance that emerges in the setting of a beta-lactam compound, (2) stable derepression due to mutations in ampC regulatory genes, or (3) the presence of plasmid-mediated ampC genes. This review will mainly focus on inducible AmpC resistance in Enterobacteriaceae. Although several observational studies have explored optimal treatment for AmpC producers, few provide reliable insights into effective management approaches. Heterogeneity within the data and inherent selection bias make inferences on effective beta-lactam choices problematic. Most experts agree it is prudent to avoid expanded-spectrum (ie, third-generation) cephalosporins for the treatment of organisms posing the greatest risk of ampC induction, which has best been described in the context of Enterobacter cloacae infections. The role of other broad-spectrum beta-lactams and the likelihood of ampC induction by other Enterobacteriaceae are less clear. We will review the mechanisms of resistance and triggers resulting in AmpC expression, the species-specific epidemiology of AmpC production, approaches to the detection of AmpC production, and treatment options for AmpC-producing infections.

Metallo-beta-lactamases (MBLs) are a significant clinical problem because they hydrolyze and inactivate nearly all beta-lactann-containing antibiotics. These 'lifesaving drugs' constitute >50% of the available contemporary antibiotic arsenal. Despite the global spread of MBLs, MBL inhibitors have not yet appeared in clinical trials. Most MBL inhibitors target active site zinc ions and vary in mechanism from ternary complex formation to metal ion stripping. Importantly, differences in mechanism can impact pharmacology in terms of reversibility, target selectivity, and structure activity relationship interpretation. This review surveys the mechanisms of MBL inhibitors and describes methods that determine the mechanism of inhibition to guide development of future therapeutics.

Introduction: Non-fermenting Gram-negative bacilli are at the center of the antimicrobial resistance epidemic. Acinetobacter baumannii and Pseudomonas aeruginosa are both designated with a threat level to human health of serious' by the Centers for Disease Control and Prevention. Two other major non-fermenting Gram-negative bacilli, Stenotrophomonas maltophilia and Burkholderia cepacia complex, while not as prevalent, have devastating effects on vulnerable populations, such as those with cystic fibrosis, as well as immunosuppressed or hospitalized patients.Areas covered: In this review, we summarize the clinical impact, presentations, and mechanisms of resistance of these four major groups of non-fermenting Gram-negative bacilli. We also describe available and promising novel therapeutic options and strategies, particularly combination antibiotic strategies, with a focus on multidrug resistant variants.Expert commentary: We finally advocate for a therapeutic approach that incorporates in vitro antibiotic susceptibility testing with molecular and genotypic characterization of mechanisms of resistance, as well as pharmacokinetics and pharmacodynamics (PK/PD) parameters. The goal is to begin to formulate a precision medicine approach to antimicrobial therapy: a clinical-decision making model that integrates bacterial phenotype, genotype and patient's PK/PD to arrive at rationally-optimized combination antibiotic chemotherapy regimens tailored to individual clinical scenarios.

Metallo-beta-lactamases (MBLs) are a significant clinical problem because they hydrolyze and inactivate nearly all beta-lactann-containing antibiotics. These 'lifesaving drugs' constitute >50% of the available contemporary antibiotic arsenal. Despite the global spread of MBLs, MBL inhibitors have not yet appeared in clinical trials. Most MBL inhibitors target active site zinc ions and vary in mechanism from ternary complex formation to metal ion stripping. Importantly, differences in mechanism can impact pharmacology in terms of reversibility, target selectivity, and structure activity relationship interpretation. This review surveys the mechanisms of MBL inhibitors and describes methods that determine the mechanism of inhibition to guide development of future therapeutics.

Introduction: Non-fermenting Gram-negative bacilli are at the center of the antimicrobial resistance epidemic. Acinetobacter baumannii and Pseudomonas aeruginosa are both designated with a threat level to human health of serious' by the Centers for Disease Control and Prevention. Two other major non-fermenting Gram-negative bacilli, Stenotrophomonas maltophilia and Burkholderia cepacia complex, while not as prevalent, have devastating effects on vulnerable populations, such as those with cystic fibrosis, as well as immunosuppressed or hospitalized patients.Areas covered: In this review, we summarize the clinical impact, presentations, and mechanisms of resistance of these four major groups of non-fermenting Gram-negative bacilli. We also describe available and promising novel therapeutic options and strategies, particularly combination antibiotic strategies, with a focus on multidrug resistant variants.Expert commentary: We finally advocate for a therapeutic approach that incorporates in vitro antibiotic susceptibility testing with molecular and genotypic characterization of mechanisms of resistance, as well as pharmacokinetics and pharmacodynamics (PK/PD) parameters. The goal is to begin to formulate a precision medicine approach to antimicrobial therapy: a clinical-decision making model that integrates bacterial phenotype, genotype and patient's PK/PD to arrive at rationally-optimized combination antibiotic chemotherapy regimens tailored to individual clinical scenarios.