Identification of two genetic groups in Bacteroides fragilis by multilocus enzyme electrophoresis: distribution of antibiotic resistance (cfiA, cepA) and enterotoxin (bft) encoding genes.

Ninety-three Bacteroides fragilis strains of different origin were analysed by multilocus enzyme electrophoresis (MLEE). Fourteen of the 15 genetic loci analysed were polymorphic, whilst nucleoside phosphorylase was monomorphic. There was a mean of six alleles per locus and a mean genetic diversity of 0.393. Cluster analysis identified 90 electrophoretic types (ETs) separated into two major phylogenetic divisions at a genetic distance of 0.70. Division I consisted of 81 ETs carrying the endogenous class A beta-lactamase gene cepA, whereas division II comprised 9 ETs carrying the class B beta-lactamase gene cfiA, but not cepA. The presence of these two genes was assessed by PCR and the expression of the cfiA gene was investigated by determining the level of resistance to the antibiotic imipenem. MLEE showed a smaller genetic distance among the genotypes of the imipenem-resistant than among the imipenem-susceptible strains. No other particular cluster was observed. The enterotoxin gene (bft) was detected by PCR: DNA sequencing of the products obtained showed that the different bft alleles (bft-1, bft-2 and bft-3) were scattered randomly troughout the phylogenetic tree. No association between distinct clones and clinical manifestations (sepsis, abscesses, diarrhoea), geographical origin or host origin (human or animal) could be found.