title: Molecular analysis of the effector mechanisms of cefoxitin resistance among Bacteroides strains.
abstract: OBJECTIVE
  The characterization of Bacteroides strains with regard to the cfxA gene, the MTn4555 mobilizable transposon, the role of penicillin-binding proteins (PBPs) and heterogeneous cefoxitin resistance.
  
  
  METHODS
  Eighty-four randomly selected and 11 heterogeneously or highly cefoxitin-resistant Bacteroides isolates were included. Agar dilution and Etest methods were used for the determination of cefoxitin MICs. PCR experiments and nucleotide sequencing were used to detect the cfxA gene and the molecular features of MTn4555. Cefoxitin-binding experiments to determine its affinity (IC(50)) for PBPs and cefoxitinase assays were also applied. Southern blotting was used to determine the copy number of the cfxA genes.
  
  
  RESULTS
  Sixteen strains from the random collection proved to be positive for cfxA, and the MIC distribution for the cfxA-negative and -positive strains did not display a clear separation. The majority of the cfxA-positive strains in this collection harboured a 1.2 kb common region at the 3' end of MTn4555. This region encoded an open reading frame that exhibited homology to abortive phage infection proteins (AbiD). The cfxA genes were transferable only at low frequencies in conjugation experiments. In PBP affinity studies, the PBP-A and PBP3 species were largely insensitive to cefoxitin, whereas the other PBP species were affected at very low concentrations. Seven of the heterogeneously resistant strains were positive for cfxA and most of them had mutations in the regulatory regions of cfxA.
  
  
  CONCLUSIONS
  Major and minor roles for Bacteroides fragilis PBPs and the CfxA cefoxitinase, respectively, were inferred. The role of the newly recognized abiD may be to control the copy number of cfxA.
authors.affiliation: Institute of Clinical Microbiology, Faculty of Medicine, Albert Szent-Györgyi Clinical Centre, University of Szeged, Szeged, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Sóki
authors.forename: Silvia Marina
authors.initials: SM
authors.lastname: Gonzalez
authors.forename: Edit
authors.initials: E
authors.lastname: Urbán
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Nagy
authors.forename: Juan Alfonso
authors.initials: JA
authors.lastname: Ayala
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001439:Bacteroides / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D001483:Base Sequence; D002440:Cefoxitin / Q000378:metabolism / Q000494:pharmacology*; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D046915:Penicillin-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D008565:Membrane Proteins; D046915:Penicillin-Binding Proteins; D002440:Cefoxitin; D001618:beta-Lactamases