title: Genetic determinants for cfxA expression in Bacteroides strains isolated from human infections.
abstract: OBJECTIVE
  To identify genetic determinants that determine beta-lactamase expression in Bacteroides strains isolated from human infections.
  
  
  METHODS
  Beta-lactam susceptibility and beta-lactamase enzyme expression were characterized in selected strains. Beta-lactamase genes and surrounding regions were analysed by PCR, inverse PCR and Southern hybridization.
  
  
  RESULTS
  High resistance to penicillins and cephalosporins was found among most isolated strains, in which all known beta-lactamase genes from Bacteroides are represented, but differences were found in their expression of enzyme activity. In contrast to the cepA gene, ubiquitously found but frequently inactive, or cfiA, which only confers carbapenem resistance in two strains, the detection of high beta-lactamase expression correlates closely with the presence of cfxA genes. This genetic determinant shares variability of upstream regulatory elements, including sequence tags from Tn4555, Tn4351 and IS614B, and polymorphisms of encoded amino acid sequences at positions G(57)C and Y(259)C, which might determine enzyme expression characteristics.
  
  
  CONCLUSIONS
  The main determinant for beta-lactamase expression in Bacteroides strains is the cfxA gene, in which IS614B integration upstream of the coding sequence represents a molecular marker for higher levels of enzyme activity.
authors.affiliation: Departamento de Medicina y Sanidad Animal, Facultad de Veterinaria, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: García
authors.forename: Gloria
authors.initials: G
authors.lastname: Gutiérrez
authors.forename: María
authors.initials: M
authors.lastname: Lorenzo
authors.forename: José E
authors.initials: JE
authors.lastname: García
authors.forename: Segundo
authors.initials: S
authors.lastname: Píriz
authors.forename: Alberto
authors.initials: A
authors.lastname: Quesada
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D001439:Bacteroides / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D001442:Bacteroides Infections / Q000382:microbiology*; D015139:Blotting, Southern; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D047090:beta-Lactams; D001618:beta-Lactamases