DETECTION OF INTESTINAL AND EXTRAINTESTINAL STRAINS OF ENTEROTOXIGENIC BACTEROIDES-FRAGILIS BY THE HT-29 CYTOTOXICITY ASSAY

Bacteroides fragilis strains with enterotoxic activity can be isolated from the faeces of newborn farm animals with diarrhoea and are called enterotoxigenic B. fragilis (ETBF). These strains can now be detected in an in-vitro cytotoxicity assay with HT-29 cells. In this study, 14 6 B. fragilis strains (95 faecal and 40 extra-intestinal isolates) and 64 Bacteroides isolates belonging to species other than B. fragilis w ere tested for their ability to produce enterotoxin. Sixteen strains o f ETBF were identified; all belonged to the fiagilis species and repre sented 11% of all B. fragilis examined. The prevalence was similar amo ng extraintestinal and faecal strains, 11.5% and 10%, respectively. Th e production of enterotoxin in clinical isolates appeared to be associ ated with infections where tissue destruction was more prominent. Ente rotoxigenicity was not associated with the presence of a plasmid and t he plasmid profiles of ETBF strains that harboured plasmids were diffe rent. These results show that enterotoxin production by human isolates of B. fragilis is not uncommon and could represent a new virulence fa ctor of B. fragilis.