Prevalence and characteristics ofEscherichia coilserotype O157:H7 and other verotoxin-producingE. coliin healthy cattle

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Abstract
Summary: From February to July of 1994, 328 faecal samples from 32 herds were collected and verotoxin-producingEscherichia coli(VTEC) found on 84% of the farms. The proportion of animals infected varied from 0–63%. VTEC were recovered from 52 (20%) of 257 cows and from 16 (23%) of 71 calves. Although the VTEC belonged to 25 different serogroups, 7 (O8. O20, O22, O77, O113, O126 and O162) accounted for 46% of strains. Nearly 45% of the 83 bovine VTEC strains belonged to serogroups associated with haemorrhagic colitis and haemolytic uraernic syndrome in humans. However, only 2 (2%) of 83 VTEC strains isolated from cattle belonged to enterohaemorrhagicE. coli(EHEC) serotypes (O26:H11 and O157:H7), and only 8 (10%) were positive for the attaching and effacingE. coli (eae)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 isolates revelated a heterogeneous population in terms of serogroup and toxin type in the positive herds. This study confirms that healthy cattle are a reservoir of VTEC, but, the absence ofeaegenes in most bovine VTEC strains suggests that they may be less virulent for humans thaneae-positive EHEC.