title: In vitro selection of variants resistant to beta-lactams plus beta-lactamase inhibitors in CTX-M beta-lactamases: predicting the in vivo scenario?
abstract: CTX-M β-lactamases are the most prevalent group of enzymes within the extended-spectrum β-lactamases (ESBL). The therapeutic options for CTX-M-carrying isolates are scarce, forcing the reexamination of the therapeutic possibilities of β-lactams plus β-lactamase inhibitors (BBLIs). Inhibitor-resistant CTX-M β-lactamases (IR-CTX-M) have not hitherto been described in natural isolates. In this study, 168 cultures of the hypermutagenic Escherichia coli GB20 strain carrying plasmid pBGS18 with different bla(CTX-M) genes were submitted to parallel experimental evolution assays in the presence of increasing concentrations of a combination of amoxicillin and clavulanate. Fourteen CTX-M β-lactamases belonging to the three most representative clusters (CTX-M-1, -2, and -9) and the two main phenotypes (cefotaxime resistance and cefotaxime-ceftazidime resistance) were studied. Three types of IR-CTX-M mutants were detected, having mutations S130G, K234R, and S237G, which are associated with different resistance patterns. The most frequently recovered mutation was S130G, which conferred the highest resistance levels to BBLIs (reaching 12 μg/ml for amoxicillin-clavulanate and 96 μg/ml for piperacillin-tazobactam when acquired by CTX-M-1 cluster enzymes). The S130G change also provided a clear antagonistic pleiotropy effect, strongly decreasing the enzyme's activity against all cephalosporins tested. A double mutation, S130G L169S, partially restored the resistance against cephalosporins. A complex pattern observed in CTX-M-58, carrying P167S and S130G or K234R changes, conferred ESBL and IR phenotypes simultaneously. The K234R and S237G changes had a smaller effect in providing inhibitor resistance. In summary, IR-CTX-M enzymes might evolve under exposure to BBLIs, and the probability is higher for enzymes belonging to the CTX-M-1 cluster. However, this process could be delayed by antagonistic pleiotropy.
authors.affiliation: Servicio de Microbiología and CIBER en Epidemiología y Salud Pública (CIBERESP), Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
authors.forename: Aida
authors.initials: A
authors.lastname: Ripoll
authors.forename: Fernando
authors.initials: F
authors.lastname: Baquero
authors.forename: Angela
authors.initials: A
authors.lastname: Novais
authors.forename: Mario J
authors.initials: MJ
authors.lastname: Rodríguez-Domínguez
authors.forename: Maria-Carmen
authors.initials: MC
authors.lastname: Turrientes
authors.forename: Rafael
authors.initials: R
authors.lastname: Cantón
authors.forename: Juan-Carlos
authors.initials: JC
authors.lastname: Galán
mesh_terms: D000658:Amoxicillin / Q000494:pharmacology; D019980:Amoxicillin-Potassium Clavulanate Combination / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002439:Cefotaxime / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology; D018550:Cephalosporin Resistance / Q000235:genetics; D019818:Clavulanic Acid / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D010878:Piperacillin / Q000494:pharmacology; D010957:Plasmids; D012641:Selection, Genetic; D000078142:Tazobactam; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D019818:Clavulanic Acid; D019980:Amoxicillin-Potassium Clavulanate Combination; D000658:Amoxicillin; D010397:Penicillanic Acid; D002442:Ceftazidime; C412613:CTX-M-9 protein, E coli; C071167:beta-lactamase CTX-2; C055184:beta-lactamase TEM-3; D001618:beta-Lactamases; D002439:Cefotaxime; D000078142:Tazobactam; D010878:Piperacillin