PREVALENCE AND CHARACTERISTICS OF ESCHERICHIA-COLI SEROTYPE O157-H7 AND OTHER VEROTOXIN-PRODUCING ESCHERICHIA-COLI IN HEALTHY CATTLE

From February to July of 1994, 328 faecal samples from 32 herds were c ollected and verotoxin-producing Escherichia coli (VTEC) found on 84% of the farms. The proportion of animals infected varied from 0-63%. VT EC were recovered from 52 (20%) of 257 cows and from 16 (23%) of 71 ca lves. Although the VTEC belonged to 25 different serogroups, 7 (O8, O2 0, O22, O77, O113, O126 and O162) accounted for 46% of strains. Nearly 45% of the 83 bovine VTEC strains belonged to serogroups associated w ith haemorrhagic colitis and haemolytic uraemic syndrome in humans. Ho wever, only 2 (2%) of 83 VTEC strains isolated from cattle belonged to enterohaemorrhagic E. coli (EHEC) serotypes (O26:H11 and O157:H7), an d only 8 (10%) were positive for the attaching and effacing E. coli (e ae) gene sequence. Polymerase chain reaction (PCR) showed that 17 (20% ) of VTEC strains carried VT1 genes, 43 (52%) possessed VT2 genes, and 23 (28%) carried both VT1 and VT2 genes. Characterization of VTEC iso lates revelated a heterogeneous population in terms of serogroup and t oxin type in the positive herds. This study confirms that healthy catt le are a reservoir of VTEC, but, the absence of eae genes in most bovi ne VTEC strains suggests that they may be less virulent for humans tha n eae-positive EHEC.