Antibiotic resistance among pathogenic bacteria is an ever-increasing issue worldwide. Unfortunately, very little has been achieved in the pharmaceutical industry to combat this problem. This has led researchers and the medical field to revisit past drugs that were deemed too toxic for clinical use. In particular, the cyclic cationic peptides polymyxin B and colistin, which are specific for Gram-negative bacteria, have been used as “last resort” antimicrobials. Before the 1980s, these drugs were known for their renal and neural toxicities; however, new clinical practices and possibly improved manufacturing have made them safer to use. Previously suggested to primarily attack the membranes of Gram-negative bacteria and to not easily select for resistant mutants, recent research exploring resistance and mechanisms of action has provided new perspectives. This review focuses primarily on the proposed alternative mechanisms of action, known resistance mechanisms, and how these support the alternative mechanisms of action.

Background: During the last decade, the prevalence of carbapenem-resistant Enterobacteriaceae in human patients has increased. Carbapenemase-producing bacteria are usually multidrug resistant. Therefore, early recognition of carbapenemase producers is critical to prevent their spread. Objectives: The objective of this study was to develop the primers for single and/or multiplex PCR amplification assays for simultaneous identification of class A, class B, and class D carbapenem hydrolyzing β-lactamases in Enterobacteriaceae and then to evaluate their efficiency. Materials and Methods: The reference sequences of all genes encoding carbapenemases were downloaded from GenBank. Primers were designed to amplify the following 11 genes: bla_KPC, bla_OXA, bla_VIM, bla_NDM, bla_IMP, bla_SME, bla_IMI, bla_GES, bla_GIM, bla_DIM and bla_CMY. PCR conditions were tested to amplify fragments of different sizes. Two multiplex PCR sets were created for the detection of clinically important carbapenemases. The third set of primers was included for detection of all known carbapenemases in Enterobacteriaceae. They were evaluated using six reference strains and nine clinical isolates. Results: Using optimized conditions, all carbapenemase-positive controls yielded predicted amplicon sizes and confirmed the specificity of the primers in single and multiplex PCR. Conclusions: We have reported here a reliable method, composed of single and multiplex PCR assays, for screening all clinically known carbapenemases. Primers tested in silico and in vitro may distinguish carbapenem-resistant Enterobacteriaceae and could assist in combating the spread of carbapenem resistance in Enterobacteriaceae. Keywords: Enterobacteriaceae; Drug Resistance; Multiplex Polymerase Chain Reaction; Carbapenems

Antibiotic resistance is an ever-increasing global problem. Major commercial antibiotics often fail to fight common bacteria, and some pathogens have become multi-resistant. Polymyxins are potent bactericidal antibiotics against gram-negative ...

Drug-resistant Klebsiella pneumoniae and related Enterobacterales represent an escalating global public health threat, increasingly limiting therapeutic options in both healthcare- and community-associated infections. This review summarizes how resistance in K. pneumoniae emerges from the synergy of intrinsic barriers and acquired determinants. Key molecular mechanisms include reduced permeability via porin remodeling (notably OmpK35/OmpK36), multidrug efflux (e.g., AcrAB-TolC and OqxAB), and enzymatic drug inactivation driven by extended-spectrum beta-lactamases and carbapenemases (e.g., KPC, OXA-48-like enzymes, and metallo-beta-lactamases). We also highlight clinically meaningful pathways underlying polymyxin/colistin resistance, including mgrB inactivation and PhoPQ/PmrAB-mediated lipid A modification. In addition to stable genetic resistance, adaptive programs can shape transient tolerance and persistence, including stress responses that modulate gene expression under antibiotic and host-imposed pressures. The ability of these organisms to form biofilms, particularly on medical devices, further complicates treatment and eradication. Finally, we discuss therapeutic implications and current options and limitations—including novel beta-lactam/beta-lactamase inhibitor combinations and siderophore cephalosporins—and emphasize the importance of aligning therapy and surveillance with the underlying resistance mechanisms and circulating high-risk lineages.

Planktonic stationary and exponential cultures of Pseudomonas aeruginosa are highly resistant to killing by bactericidal antimicrobials because of the presence of persisters, cells that are multidrug tolerant and play a key role in the recalcitrance of biofilm infections. The aim of this study was to investigate the formation of persister cells in P. aeruginosa stationary vs. exponential cultures using different class antimicrobials. The susceptibilities of P. aeruginosa PAO1 wild-type and mutant strains to antimicrobials were determined by standard microtiter broth dilution method. In order to determine persister formation, dose- and time-dependent killing experiments were performed with antibiotics. Ceftazidime (Cephalosporin) showed little efficacy against either culture. Stationary-phase cells were more tolerant to imipenem (Carbapenem) than exponential cells, leaving a small fraction of persisters at high imipenem concentration in both populations. Polymyxin B (Polymyxin) appeared to be ineffective at low concentrations against both cell populations. Very high polymyxin B concentration completely eradicated exponential cells and regrowth was seen in a stationary population. Stationary cells were more tolerant to tobramycin (Aminoglycoside) than exponential cells but a higher concentration of tobramycin completely eliminated survivors. Ciprofloxacin (Fluoroquinolone) at a low concentration resulted in killing of both cultures of P. aeruginosa, producing persisters that were invulnerable to killing. Stationary cells appear to be somewhat more tolerant than exponential cells in all of these assays. We also showed that nutrient deprivation (serine starvation) regulated by stringent and general stress response, contribute to the increased tolerance of P. aeruginosa exponential and stationary planktonic cells via production of persisters.

The relative inhibitory activities of diazabicyclooctanes (avibactam, relebactam, zidebactam, nacubactam, durlobactam), boronic acid derivatives (vaborbactam, taniborbactam, xeruborbactam), and penicillin-based sulfone derivative enmetazobactam were evaluated against several intrinsic and acquired class C β-lactamases. By contrast to vaborbactam and enmetazobactam, taniborbactam, xeruborbactam, and all diazabicyclooctanes demonstrated effective activities against most AmpC enzymes. Notably, durlobactam exhibited the most pronounced inhibitory effect. Interstingly, the chromosomal AmpC of Acinetobacter baumannii was the least sensitive enzyme to the newly developed β-lactamase inhibitors.