Virulence factors and biochemical characteristics of serotypes of Escherichia coli serogroup O29.

Escherichia coli strains belonging to serogroup O29 were studied. Invasiveness was the most common virulence factor described in this serogroup, but a few papers also reported production of heat-stable (ST) enterotoxin. In the present study invasive ability was found in O29:H- strains, whereas production of ST-I enterotoxin was observed only in serotype O29:H21 strains, showing that virulence was a characteristic of specific serotypes or bioserotypes within the O29 serogroup. Different serotypes were found among strains that were neither invasive nor toxigenic. Invasive strains were biochemically less active than the toxigenic ones and presented the invasiveness plasmid (pINV) of about 120 to 140 megadaltons, whereas hybridization tests showed that ST-I production was related to a plasmid of about 90 megadaltons. A diffuse adherence pattern to HeLa cells was observed in all ST-I isolates, but the role of this adherence in the pathogenicity of these strains was not determined. Thus, a unique biochemical pattern and plasmid profile may be useful characteristics to distinguish between pathogenic (toxigenic or invasive) and nonpathogenic O29 strains.