Isolation of verocytotoxin-producing Escherichia coli from milk filters in south-western Ontario.

A total of 1012 milk filters collected from 498 dairy farms in south-western Ontario during three study periods (December 1985-March 1986) were tested for the presence of verocytotoxin-producing Escherichia coli (VTEC). VTEC were detected and isolated using a Vero cell assay. Supernatants from 20 of the milk filter cultures had verocytotoxic activity and 7 VTEC strains were isolated from these positive samples. The prevalence of VTEC in the samples in each of the three study periods were 0.44, 0.65 and 0.99% respectively. All seven VTEC strains isolated were sensitive to commonly used antimicrobial agents. The serotypes of these strains were O 26.H11, O43.H2, O 153.H25, O ?. H8, O? .H19, O ?. non-motile, and Orough.H19. Two of these serotypes (O 153.H25 and O 26.H11) have previously been associated with disease in humans.