Prevalence and characteristics of necrotoxigenic Escherichia coli CNF1+ and CNF2+ in healthy cattle.

From February to July of 1994, 328 faecal samples from 32 herds were collected and examined for necrotoxigenic Escherichia coli (NTEC). Strains producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2) were found on 4 and 63% of the farms, respectively. The proportion of animals infected within each herd varied from 0 to 38%. NTEC producing CNF2 were significantly more frequently isolated from calves (24%; 17 of 71) than from cows (4%; 11 of 257) (chi 2corr. 25.088; P < 0.001). Although the bovine CNF2+ strains belonged to 16 different serogroups, 5 (O15, O77, O88, O142 and O153) accounted for 44% of strains. This study confirmed that healthy cattle are a reservoir of NTEC producing CNF2, and revealed that CNF2+ strains are more frequently carried by calves than by adult cows.