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Diarrhoeic stool samples from 334 0-5-year-old children were analysed with respect to the incidence of Bacteroides fragilis as well as other enteropathogens. B. fragilis was recovered in 9.3% (31/334) of the samples, and 79 strains were examined for the presence of the bft gene or the BfPAI flanking region using polymerase chain reaction assays. No enterotoxigenic B. fragilis strains were detected. In 29% (9/31) of the samples the coexistence of both II and III non-toxigenic B. fragilis (NTBF) patterns could be seen. In 51.6% (16/31) of the samples there existed a pattern II NTBF only, and in 19.4% (6/31) only pattern III could be detected. Strains from the same patient representing different patterns were submitted to pulsed-field gel electrophoresis assays. Fingerprints obtained by this technique showed that there was strong heterogeneity among strains from different individuals. However, different patterns from the same individual shared 100% similarity.

Bacteroides fragilis is a component of the normal intestinal flora and an important pathogen in nonintestinal endogenous infections. It has been associated with enteric infections and has already been detected in polluted water. In order to evaluate the genetic diversity of B. fragilis, a total of 31 isolates and two reference strains were examined. This collection included strains from nonintestinal infections [12], intestinal infections [5], intestinal microflora [10], aquatic environments [4], and the reference strains ATCC 25285 and ATCC 23745. DNA fingerprints were detected using two separate PCR reactions with different arbitrary primers. The computer-assisted system Taxotron (Institut Pasteur, Dr P. Grimont) was used to analyze the profiles obtained and dendrograms were generated. By using a distance of 0.65 as the threshold, two clusters (hereafter referred to as genotypes I and II) were defined. Strains of differents origins could be distributed into both genotypes. We were unable to detect any obvious correlation between a given genotype and the specific disease or the source of the corresponding strains.

We have demonstrated that pure cultures of Bacteroides fragilis can be riboprobed with the oligoprobes BAC303 and EUB338, whilst simultaneously immunolabelled with either the mAb QUBF7, or polyclonal antiserum specific for a common antigen of B. fragilis. We were also able to distinguish between pure cultures of B. fragilis and Escherichia coli, by means of combined immunolabelling and riboprobing. The success of the combined technique is critically dependent on the size of the bacterial capsules, bacterial growth phase, antibody diluent and the length of the washing steps. The combined FISH and immunolabelling of bacteria has potential applications in studies of bacteria of medical and veterinary importance, as well as bacteria from other environments, as it yields information about both the identity and antigen expression of individual bacterial cells.