Expression of Bacteroidos fragilis virulence markers in vitro

Bacteroides fragilis isolates from intestinal and non-intestinal infections , normal flora and the environment were examined for properties linked with interactions among cells in vitro. Different adhesion molecules were detec ted in agglutination assays with human erythrocytes and tests for auto-aggl utination and adherence to human colon carcinoma cells (HT29), There was no correlation between these properties, indicating that independent molecule s are involved, Treatment with trypsin, heat or EDTA inhibited agglutinatio n and adherence, suggesting that these molecules are proteins. The lack of correlation with the origin of the strains did not permit any of these acti vities to be recognised as virulence markers. The expression of fragilysin, a protease associated with damage to intestinal cells and bacterial transl ocation, was examined, Only those strains from patients with diarrhoea expr essed this protease activity in assays with HT29 cells and this was confirm ed by specific PCR far the bft gene. The activity of fragilysin as an enter otoxin was confirmed in the rabbit intestinal ligated loop assay. The assoc iation of this property only with strains from intestinal infections indica tes that it is too early to suggest this protease as a determinant factor o f B. fragilis invasiveness.