Study of polymorphisms in tir, eae and tccP2 genes in enterohaemorrhagic and enteropathogenic Escherichia coli of serogroup O26.

Background: Enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) Escherichia coli are responsible for food poisoning (enteritis and enterotoxaemia) in humans in developed countries. Cattle are considered to be an important reservoir of EHEC and EPEC strains for humans. Moreover, some of the strains, belonging to the O26, O111, O118 serogroups, for example, are also responsible for digestive disorders in calves. The Translocated intimin receptor (Tir), the intimin (Eae) and the Tir-cytoskeleton coupling protein (TccP) represent three virulence factors implicated in the intimate attachment of the bacteria to the eukaryotic cell. Major variants have already been described for these genes among the different serogroups but minor variations have not often been studied. In this study, we examined the polymorphisms of the tir, eae and tccP2 genes of O26 strains (EPEC and EHEC isolated from bovines and from humans) with the aim to determine whether these polymorphisms are host specific or not.

Results: Of the 70 tested strains, 10 strains (14% of the strains) presented one or several polymorphisms in the tir and eae genes, which have never previously been described. Concerning tccP2 detection, 47 of the 70 strains (67% of the strains) were found to be positive for this gene. Most of the strains were found to possess tccP2 variants described in strains of serogroup O26. Nevertheless, three strains had tccP2 genes respectively described in strains of serogroup O111, O103 and O55. Moreover, none of the polymorphisms was statistically specific to the bovine or the human isolates. Nevertheless, the two major variants of tccP2 were statistically associated with the pathotype (EPEC or EHEC).

Conclusions: In conclusion, tir and eae gene polymorphisms were found not to be numerous and not to be predominantly synonymous. Moreover, no difference was observed between human and bovine strains regarding the presence of polymorphisms. Finally, some tccP2 variants appeared to be pathotype specific. Further investigations need to be performed on a larger number of strains in order to confirm this specificity.