Characterization of indole-negative Bacteroides fragilis group species with use of polymerase chain reaction fingerprinting and resistance profiles.

Biochemical tests alone do not adequately differentiate the various Bacteroides species, groups, and antimicrobial-resistant variants. Consequently, we used a polymerase chain reaction (PCR) fingerprinting technique, with either a single nonspecific primer derived from the t-DNA intergenic spacer region (T3B) or a single primer that anneals to minisatellite DNA sequences (M13 core), to identify and characterize 58 clinical isolates of Bacteroides fragilis group species (B. fragilis, B. distasonis, and B. caccae). In addition to species- and subspecies-specific differences, 4 strains of B. fragilis, 1 of B. distasonis, and 3 of B. caccae that showed increased resistance to imipenem, ampicillin, and ampicillin/sulbactam also produced unique PCR fingerprint profiles. Analysis by the clinical source of isolation (i.e. blood or intraabdominal, skin, or soft-tissue infection) indicated that no particular PCR fingerprint type was associated with greater pathogenicity of any individual clinical source. The PCR fingerprinting technique proves to be a useful tool for species identification and taxonomic studies, as well as for epidemiological studies of Bacteroides species.