AmpC
Mechanisms of ResistanceCeftazidime-Avibactam Resistance Mediated by the N346Y Substitution in Various AmpC β-LactamasesChromosomal and plasmid-borne AmpC cephalosporinases are a major resistance mechanism to β-lactams in Enterobacteriaceae and Pseudomonas aeruginosa. The new β-lactamase inhibitor avibactam effectively inhibits class C enzymes and can fully restore ceftazidime susceptibility. The conserved amino acid residue Asn346 of AmpC cephalosporinases directly...
Mechanisms of ResistanceHypermutator Pseudomonas aeruginosa Exploits Multiple Genetic Pathways To Develop Multidrug Resistance during Long-Term Infections in the Airways of Cystic Fibrosis PatientsPseudomonas aeruginosa exploits intrinsic and acquired resistance mechanisms to resist almost every antibiotic used in chemotherapy. Antimicrobial resistance in P. aeruginosa isolates recovered from cystic fibrosis (CF) patients is further enhanced by the occurrence of hypermutator strains, a...
Editor's Pick Mechanisms of ResistanceA Standard Numbering Scheme for Class C β-LactamasesUnlike for classes A and B, a standardized amino acid numbering scheme has not been proposed for the class C (AmpC) β-lactamases, which complicates communication in the field. Here, we propose a scheme developed through a collaborative approach that considers both sequence and structure, preserves traditional numbering of catalytically important residues (Ser64, Lys67, Tyr150, and Lys315), is...
Editor's Pick Mechanisms of ResistanceA 2.5-Year Within-Patient Evolution of Pseudomonas aeruginosa Isolates with In Vivo Acquisition of Ceftolozane-Tazobactam and Ceftazidime-Avibactam Resistance upon TreatmentCeftolozane-tazobactam is considered to be a last-resort treatment for infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa. Although resistance to this antimicrobial has been described in vitro, the development of resistance in vivo has rarely been reported. Here, we describe the evolution of resistance to ceftolozane-tazobactam of...
Mechanisms of ResistanceFirst Clinical Case of In Vivo Acquisition of DHA-1 Plasmid-Mediated AmpC in a Salmonella enterica subsp. enterica IsolateA pan-susceptible Salmonella enterica serovar Worthington isolate was detected in the stool of a man returning from Sri Lanka. Under ceftriaxone treatment, a third-generation cephalosporin (3GC)-resistant Salmonella Worthington was isolated after 8 days. Molecular analyses indicated that the two isolates were identical. However, the latter strain acquired a...
Mechanisms of ResistanceGenomic Analysis Identifies Novel Pseudomonas aeruginosa Resistance Genes under Selection during Inhaled Aztreonam Therapy In VivoInhaled aztreonam is increasingly used for chronic Pseudomonas aeruginosa suppression in patients with cystic fibrosis (CF), but the potential for that organism to evolve aztreonam resistance remains incompletely explored. Here, we performed genomic analysis of clonally related pre- and posttreatment CF clinical isolate pairs to identify genes that are under positive...
Mechanisms of ResistanceDefects in Efflux (oprM), β-Lactamase (ampC), and Lipopolysaccharide Transport (lptE) Genes Mediate Antibiotic Hypersusceptibility of Pseudomonas aeruginosa Strain Z61Antibiotic hypersensitive bacterial mutants (e.g., Escherichia coli imp) are used to investigate intrinsic resistance and are exploited in antibacterial discovery to track weak antibacterial activity of novel inhibitor compounds. Pseudomonas aeruginosa Z61 is one such drug-hypersusceptible...
Mechanisms of ResistanceFalse-Positive Carbapenem-Hydrolyzing Confirmatory Tests Due to ACT-28, a Chromosomally Encoded AmpC with Weak Carbapenemase Activity from Enterobacter kobeiIn Enterobacter cloacae complex (ECC), the overproduction of the chromosome-encoded cephalosporinase (cAmpC) associated with decreased outer membrane permeability may result in carbapenem resistance. In this study, we have characterized ACT-28, a cAmpC with weak carbapenemase activity, from a single ...
Mechanisms of ResistanceCirculation of Plasmids Harboring Resistance Genes to Quinolones and/or Extended-Spectrum Cephalosporins in Multiple Salmonella enterica Serotypes from Swine in the United StatesNontyphoidal Salmonella enterica (NTS) poses a major public health risk worldwide that is amplified by the existence of antimicrobial-resistant strains, especially those resistant to quinolones and extended-spectrum cephalosporins (ESC). Little is known on the dissemination of plasmids harboring the acquired genetic determinants that confer resistance to these...
