Stool samples from children and adults with and without diarrhea were examined for the presence of enterotoxigenic Bacteroides fragilis (ETBF) and its enterotoxin. A cytotoxic assay with HT-29 cells followed by neutralization with a hyperimmune antiserum were used to detect B. fragilis enterotoxin. ETBF isolates were recovered from 12% of healthy children and 17% of children with diarrhea (P = .42) and from 15% of healthy adults and 9.4% of adults with diarrhea (P = .31). Fecal B. fragilis enterotoxin was detected in four children (two with diarrhea and two without diarrhea) and in four adults with diarrhea. This study shows that in Italy, the rate of ETBF carriage is high, regardless if diarrhea is present. In some instances, the presence of ETBF is associated with detectable levels of fecal enterotoxin, but the significance of this finding deserves further evaluation.

Strains of enterotoxigenic Bacteroides fragilis (ETBF) are associated with diarrhea in young farm animals and, at least in particular settings, in children. Enterotoxin production by ETBF is currently detected by a tissue culture assay with HT-29 cells. We have developed a PCR assay based on the detection of the enterotoxin gene to identify ETBF in culture and in stool samples. Overall, 113 bacterial strains were examined, including 3 B. fragilis reference strains, 75 B. fragilis isolates (comprising 40 ETBF isolates), 20 Bacteroides spp. other than B. fragilis, and 15 strains belonging to other genera. Complete agreement was found between the results of the tissue culture assay and those of the PCR for our strains. PCR was also used to detect ETBF directly in fecal samples. Stools from two healthy volunteers were spiked with known numbers of ETBF and were processed by three different methods. A culture method, which required inoculation of the stools on selective plates and the collection of the whole bacterial growth ("sweeps"), was found to be the most sensitive. PCR performed with the plate sweeps yielded amplification products with a detection limit of 10 5 to 10 4 CFU/g of feces. By this method 18 samples of diarrheic stools (10 positive and 8 negative for ETBF) were examined. The results of the PCR were in accordance with the culture results in all cases. The proposed PCR assay represents a diagnostic tool for the rapid identification of ETBF in culture as well as in fecal samples.

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