PREVALENCE OF THE EAEA GENE IN VEROTOXIGENIC ESCHERICHIA-COLI STRAINSFROM DAIRY-CATTLE IN SOUTHWEST ONTARIO

This study determined the prevalence of the eaeA gene and its relation ship to serotype and type of verotoxin produced in a collection of 432 verotoxigenic Escherichia coli (VTEC) obtained from the faeces of hea lthy cows and calves in a systematic random survey involving 80 dairy farms in Southwest Ontario. A PCR amplification procedure involving pr imer pairs which target the conserved central region of the O157:H7 ea eA gene showed that 151 (35.2%) strains were positive for the eaeA gen e. All isolates (9-21 for each O group) of O groups 5, 26, 69, 84, 103 , 111, 145 and 157 were positive, whereas all isolates (7-34 for each O group) of O groups 113, 132, and 153 and serotype O156:NM (38 isolat es) were negative for eaeA. Seventy-three percent of 130 isolates of e aeA-positive serotypes produced VT1 only compared with 20% of 253 isol ates of eaeA-negative serotypes. We conclude that there is a strong as sociation between certain O groups and the eaeA gene, that serotypes o f eaeA-positive and eaeA-negative VTEC implicated in human and cattle disease are present at high frequency in the faeces of healthy cattle, that VT1 is more frequently associated with eaeA-positive than with e aeA-negative serogroups, and that the eaeA gene is more frequently fou nd in VTEC from calves compared with VTEC from adult cattle.