Prevalence, characterization and clonal analysis of Escherichia coli O157: non-H7 serotypes that carry eae alleles

We examined O157:non-H7 strains isolated from various sources and geographical locations and found 15/57 strains to carry eae alleles, including alpha, beta, epsilon and kappa/delta, suggesting that these strains may be prevalent. All strains were serologically and genetically confirmed to be O157, but none were the H7 serotype or carried any trait virulence factors of the Escherichia coli O157:H7 serotype. Genetic H typing of the eae-positive strains showed that the alpha-eae-bearing strain was H45, while the beta- and epsilon-eae strains were H16 and the kappa/delta-eae strains were H39. The beta- and epsilon-eae-bearing O157:H16 strains shared approximately 90% pulsed-field gel electrophoresis (PFGE) similarity and were distinct from the other strains that had other eae alleles. Interestingly, an epsilon-eae O157:H16 strain isolated from meat in France shared PFGE similarity to the O157:H16 strains from water in the United States. Multilocus sequence typing showed that there is clonal diversity within the O157 serogroup, as some O157:non-H7 strains clustered with EPEC clonal groups, while others clustered within the ST-171 group of diverse strains and serotypes that had not previously included any strains from the O157 serogroup. Clonal analysis also showed that none of the eae-positive O157:non-H7 strains we examined were closely related to the pathogenic O157:H7 serotype.