First isolation and further characterization of enteropathogenic Escherichia coli (EPEC) O157:H45 strains from cattle

Abstract

Background: Enteropathogenic Escherichia coli (EPEC), mainly causing infantile diarrhoea, represents one of at least six different categories of diarrheagenic E. coli with corresponding distinct pathogenic schemes. The mechanism of EPEC pathogenesis is based on the ability to introduce the attaching-and-effacing (A/E) lesions and intimate adherence of bacteria to the intestinal epithelium. The role and the epidemiology of non-traditional enteropathogenic E. coli serogroup strains are not well established. E. coli O157:H45 EPEC strains, however, are described in association with enterocolitis and sporadic diarrhea in human. Moreover, a large outbreak associated with E. coli O157:H45 EPEC was reported in Japan in 1998. During a previous study on the prevalence of E. coli O157 in healthy cattle in Switzerland, E. coli O157:H45 strains originating from 6 fattening cattle and 5 cows were isolated. In this study, phenotypic and genotypic characteristics of these strains are described. Various virulence factors (stx, eae, ehxA, astA, EAF plasmid, bfp) of different categories of pathogenic E. coli were screened by different PCR systems. Moreover, the capability of the strains to adhere to cells was tested on tissue culture cells.

Results: All 11 sorbitol-positive E. coli O157:H45 strains tested negative for the Shiga toxin genes (stx), but were positive for eae and were therefore considered as EPEC. All strains harbored eae subtype alpha1. The gene encoding the heat-stable enterotoxin 1 (EAST1) was found in 10 of the 11 strains. None of the strains, however, carried ehx A genes. The capability of the strains to adhere to cells was shown by 10 strains harbouring bfp gene by localized adherence pattern on HEp-2 and Caco-2 cells.

Conclusion: This study reports the first isolation of typical O157:H45 EPEC strains from cattle. Furthermore, our findings emphasize the fact that E. coli with the O157 antigen are not always STEC but may belong to other pathotypes. Cattle seem also to be a reservoir of O157:H45 EPEC strains, which are described in association with human diseases. Therefore, these strains appear to play a role as food borne pathogens and have to be considered and evaluated in view of food safety aspects.

Figure 1

Localized adherence (LA) pattern of the E. coli O157:H45 strain 1070/03 on HEp-2 cells. (a) 3 h assay, (b) 6 h assay

Figure 2

Localized adherence (LA) pattern of the E. coli O157:H45 strain 1070/03 on Caco-2 cells. (a) 3 h assay, (b) 6 h assay

Figure 3

Actin fluorescence micrograph showing E. coli O157:H45 strain 1070/03-infected Caco-2 cells