AmpC
SusceptibilityEmergence of Resistance in Klebsiella aerogenes to Piperacillin-Tazobactam and CeftriaxoneWe examined the effects of piperacillin-tazobactam (TZP) concentration and bacterial inoculum on in vitro killing and the emergence of resistance in Klebsiella aerogenes. The MICs for 15 clinical respiratory isolates were determined by broth microdilution for TZP and by Etest for ceftriaxone (CRO) and cefepime (FEP). The presence of resistance in TZP-...
Clinical TherapeuticsIs Ceftazidime/Avibactam an Option for Serious Infections Due to Extended-Spectrum-β-Lactamase- and AmpC-Producing Enterobacterales?: a Systematic Review and Meta-analysisCarbapenem-sparing regimens are needed for the treatment of infections caused by extended-spectrum-β-lactamase (ESBL)- and AmpC-producing members of the Enterobacterales. We sought to compare the clinical efficacy of ceftazidime/avibactam and carbapenems against ESBL- and AmpC-producing Enterobacterales species. A systematic review and meta-analysis of randomized controlled trials comparing ceftazidime/avibactam with...
Epidemiology and SurveillanceEscherichia coli Sequence Type 457 Is an Emerging Extended-Spectrum-β-Lactam-Resistant Lineage with Reservoirs in Wildlife and Food-Producing AnimalsSilver gulls carry phylogenetically diverse Escherichia coli, including globally dominant extraintestinal pathogenic E. coli (ExPEC) sequence types and pandemic ExPEC-ST131 clades; however, our large-scale study (504 samples) on silver gulls nesting off the coast of New South Wales identified...
Editor's Pick Mechanisms of ResistanceAdding Insult to Injury: Mechanistic Basis for How AmpC Mutations Allow Pseudomonas aeruginosa To Accelerate Cephalosporin Hydrolysis and Evade AvibactamPseudomonas aeruginosa is a leading cause of nosocomial infections worldwide and notorious for its broad-spectrum resistance to antibiotics. A key mechanism that provides extensive resistance to β-lactam antibiotics is the inducible expression of AmpC β-lactamase. Recently, a number of clinical isolates expressing mutated forms of AmpC have been found to be clinically...
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...
