Identification of two genetic groups in Bacteroides fragilis by multilocusenzyme 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 lo ci analysed were polymorphic, whilst nucleoside phosphorylase was monomorph ic. There was a mean of six alleles per locus and a mean genetic diversity of 0.393. Cluster analysis identified 90 electrophoretic types (ETs) separa ted into two major phylogenetic divisions at a genetic distance of 0.70. Di vision 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-l actamase gene cfiA, but not cepA. The presence of these two genes was asses sed by PCR and the expression of the cfiA gene was investigated by determin ing the level of resistance to the antibiotic imipenem. MLEE showed a small er genetic distance among the genotypes of the imipenem-resistant than amon g the imipenem-susceptible strains. No other particular cluster was observe d. The enterotoxin gene (bft) was detected by PCR: DNA sequencing of the pr oducts 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, di arrhoea), geographical origin or host origin (human or animal) could be fou nd.