Identification of two genetic groups in Bacteroides fragilis by multilocus enzyme electrophoresis: distribution of antibiotic resistance (cfiA, cepA) and enterotoxin (bft) encoding genes The GenBank accession numbers for the sequences determined in this work are AF197508–AF197534.

Abstract

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 0393. Cluster analysis identified 90 electrophoretic types (ETs) separated into two major phylogenetic divisions at a genetic distance of 070. Division I consisted of 81 ETs carrying the endogenous class A β-lactamase gene cepA, whereas division II comprised 9 ETs carrying the class B β-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.

recA and glnA sequences separate the Bacteroides fragilis population into two genetic divisions associated with the antibiotic resistance genotypes cepA and cfiA

“…Isolates encoding the B. fragilis bft enterotoxin genes (determined by PCR assays [3]) were all in division I, but they were not associated with a particular subgroup within the division.…”

“…A total of 45 B. fragilis strains originating from different countries, one Bacteroides ovatus, and one Bacteroides uniformis was chosen from the sample collection, which was previously investigated by MLEE [3]. This collection included human invasive and non-invasive (recovered from patients' stools) strains from different geographical regions (Switzerland, France, Norway, USA and Japan), strains producing enterotoxin, invasive isolates from animals and one reference strain (ATCC 25285) of B. fragilis (Table 1).…”

“…This collection included human invasive and non-invasive (recovered from patients' stools) strains from different geographical regions (Switzerland, France, Norway, USA and Japan), strains producing enterotoxin, invasive isolates from animals and one reference strain (ATCC 25285) of B. fragilis (Table 1). Bacteria were grown, identi®ed and stored as described previously [3]. B. ovatus and B. uniformis were used as outgroup strains in the recA analysis, whereas no outgroup sequences were available for the glnA gene.…”

“…A fragment of 353 bp of the c®A gene was ampli®ed with primers c®A-1 and c®A-2 as described previously [3]. …”

“…Occasionally, some strains produce an enterotoxin [1,2]. Studies with multilocus enzyme electrophoresis (MLEE) [3] and other molecular techniques ± particularly 16S rRNA sequencing [4] and DNA±DNA hybridisation [5] ± have shown the separation of the population into two groups presenting an extensive genetic distance one from the other (divisions I and II). Division I was characterised by the frequent presence of the cepA gene (encoding a serine-â-lactamase of Ambler's class A) and the absence of the c®A gene (encoding a metallo-â-lactamase of Ambler's class B).…”