title: Mutagenesis of the CTX-M-type ESBL-is MIC-guided treatment according to the new EUCAST recommendations a safe approach?
abstract: OBJECTIVE
  Spurred by the latest EUCAST and CLSI recommendation to adjust antibiotic therapy on the basis of MICs instead of resistance mechanisms, we aimed to investigate the ability of CTX-M-1 and CTX-M-14 to achieve ceftazidime resistance under selective conditions.
  
  
  METHODS
  We exposed Escherichia coli transconjugants bearing natural plasmids that express CTX-M-1, CTX-M-14 or CTX-M-15 to various selective culture conditions and tracked their growth and mutational frequencies. For selected mutants we analysed the sequences of the bla CTX-M genes, determined the altered MICs of cefotaxime, cefepime, ceftazidime and meropenem, and measured the efflux properties and the changes in transcriptional levels of bla CTX-M genes.
  
  
  RESULTS
  The CTX-M-1- and CTX-M-14-bearing clones switched from ceftazidime-susceptible to ceftazidime-resistant phenotypes under selective conditions within 24 h. However, no mutations within the bla CTX-M genes were found, and the efflux was unlikely to be involved in the increased ceftazidime MICs. In CTX-M-1-bearing clones bla CTX-M-1 expression was 19-fold increased under ceftazidime-selective conditions but there was a high variance within the clones. Reasons for increased ceftazidime MICs of CTX-M-bearing clones remain unclear but might be the increased enzymatic activity or other intrachromosomal mutations.
  
  
  CONCLUSIONS
  It can be speculated that different strategies to survive under selective conditions can be adopted by E. coli, thereby establishing an optimal mechanism with the lowest energy demand for each transconjugant. Based on our in vitro findings, we cannot fully recommend the use of ceftazidime, particularly in critically ill patients with infections due to ESBL producers, regardless of susceptibility to ceftazidime.
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: João M
authors.initials: JM
authors.lastname: Costa Ramos
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Stein
authors.affiliation: Nosocomial Pathogens and Antibiotic Resistance, Robert Koch Institute, Burgstrasse 37, D-8855 Wernigerode, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Pfeifer
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Brandt
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: Mathias W
authors.initials: MW
authors.lastname: Pletz
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany oliwia.makarewicz@med.uni-jena.de.
authors.forename: Oliwia
authors.initials: O
authors.lastname: Makarewicz
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D020869:Gene Expression Profiling; D006801:Humans; D008826:Microbial Sensitivity Tests; D016296:Mutagenesis; D059645:Mutation Rate; D010957:Plasmids; D017410:Practice Guidelines as Topic; D012641:Selection, Genetic; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; C456080:beta-lactamase CTX-M-14; C473109:beta-lactamase CTX-M-15; C055184:beta-lactamase TEM-3; D001618:beta-Lactamases