Survey of clinical isolates of diarrhoeogenic Escherichia coli: diffusely adhering E. coli strains with multiple adhesive factors.

Abstract

A total of 335 Escherichia coli strains were isolated from sporadic cases of aqueous diarrhoea in patients hospitalized in Clermont-Ferrand, France, during 1991 and 1992. Many of these strains belonged to the diffusely adhering E. coli (DAEC) group, since 51 of them (15.2%) hybridized with the daaC probe corresponding to the accessory gene of the F1845 adhesin and 13 (3.9%) with the AIDA-I (adhesin involved in diffuse adhesion-I) structural gene. The other pathogenic E. coli groups were weakly represented: 0.6% (2 strains) of enterotoxigenic E. coli (ETEC), 0.6% (2 strains) of enterohaemorrhagic E. coli (EHEC) and 3.9% (13 strains) of enteroaggregative E. coli (EAggEC). Neither enteropathogenic E. coli (EPEC) nor enteroinvasive E. coli (EIEC) were isolated in our study period. Among the DAEC strains studied, we described two major surface proteins of 16 and 29 kDa. We showed that the 16-kDa protein (CF16K) was involved in adhesion in vitro to Caco-2 and HEp-2 cells. Pretreatment of bacteria with anti-CF16K serum or of Caco-2 cells with purified CF16K greatly decreased the adhesion of the E. coli CF1085 strain producing the CF16K protein to both cell types. The CF16K adhesive factor was found in 9.5% (33 strains) of the 335 E. coli strains studied by colony immunoblot assays with anti-CF16K serum. Twelve strains producing CF16K hybridized with the daaC probe, indicating that the CF16K is not related to the Dr family adhesins which recognized the Dr blood group antigen as receptor. The 29-kDa protein, isolated from 9 strains out of the 335 studied (5.1%), was identified as the CS31A antigen by Western blot assay using anti-CS31A serum and by hybridization experiments with a CS31A DNA probe. This antigen is routinely observed in septicaemic or enterotoxigenic bovine E. coli strains. We showed that a single diarrhoeogenic E. coli strain could harbour at least two adhesive factors, since 36% of CF16K E. coli strain producers and 68.4% of CS31A E. coli strain producers hybridized with the daaC DNA probe.