GENOTYPIC IDENTIFICATION OF 2 GROUPS WITHIN THE SPECIES BACTEROIDES-FRAGILIS BY RIBOTYPING AND BY ANALYSIS OF PCR-GENERATED FRAGMENT PATTERNS AND INSERTION-SEQUENCE CONTENT

Molecular typing allowed the separation of the species Bacteroides fra gilis into two genotypically distinct groups. A unique set of 50 strai ns of B. fragilis carrying the chromosomal metallo-beta-lactamase gene cfiA was subjected to a comparative analysis with respect to sets of up to 250 randomly collected strains devoid of this gene. The two grou ps were found to be distinct on the basis of the following results: (i ) ribotyping, after DNA digestion with AvaI, revealed a practically ho mogeneous DNA fragment pattern for the cfiA-positive strains and disti nct multiple patterns for the cfiA-negative strains; (ii) PCR, arbitra rily primed with an experimentally selected decamer, generated fragmen t patterns typical for the strains of each group; (iii) the three inse rtion sequences described to date in the species B. fragilis, i.e., IS 4351, IS942, and IS1186, were all but confined to the cfiA-positive gr oup, in which they were capable of providing promoter sequences for th e transcription of cfiA; and (iv) the cepA gene, encoding the so-calle d endogenous cephalosporinase of B. fragilis was found exclusively in the cfiA-negative group, in which it was present in ca. 70% of the str ains. The cfiA-, cepA-negative fraction was not characterized Further. In a natural population of 500 randomly selected strains of B. fragil is, the cfiA positive and cfiA-negative groups represented ca. 3 and 9 7% of the strains, respectively. Analysis of 82 metabolic traits revea led no difference between the two groups.