PREVALENCE AND CHARACTERISTICS OF STRAINS OF ESCHERICHIA-COLI ISOLATED FROM MILK AND FECES OF COWS ON DAIRY FARMS IN TRINIDAD

The prevalence, counts, and characteristics of Escherichia coli isolat ed from hulk milk, composite milk, and feces of dairy cows in eight mi lking centers were determined. The microbial quality of water used dur ing milking was also investigated. Of a total of 175 bulk milk samples studied, 83 (47.4%) contained E. coli compared to only 14 (4.9%) of 2 87 composite milk samples and the difference was statistically signifi cant (P less than or equal to 0.001; chi(2)). The ranges in mean count s of E. coli per milliliter of hulk milk and composite milk were 8.4 X 10(3) to 2.0 X 10(5) and 2.1 X 10(1) to 2.0 X 10(2), respectively. Th e prevalences and mean counts of E. coli and mean pH values for bulk m ilk from farms with and without subclinically mastitic cows were not s ignificantly different (P greater than or equal to 0.05; chi(2)). A to tal of 204 (65.2%) of 313 fecal samples of dairy cows were positive fo r E. coli. Of the samples of water used during milking collected from 171 dairy farms, 80 (46.8%) were free of coliforms while 59 (34.5%), 1 2 (7.0%), and 8 (4.7%) had ranges of coliform counts per 100 ml of 1 t o 50, 51 to 100, and over 250, respectively. Twenty-six (27.7%) and 17 (18.5%) of 94 strains of E. coli isolated from bulk milk were enterop athogenic E. coli (EPEC) and verocytotoxigenic E. coli (VTEC) strains, respectively. Compared with 204 fecal strains of E. coli, 16 (7.8%) a nd 68 (35.6%) were EPEC and VTEC strains, respectively, and the differ ences were statistically significant (P less than or equal to 0.01; ch i(2)). Similarly, the difference in prevalence of resistance to one or more of nine antimicrobial agents between bulk milk isolates (69.6%) and fecal isolates (25.9%) was statistically significant (P less than or equal to 0.001; chi(2)), and resistance to ampicillin was the most prevalent type of resistance for strains of E. coli from bulk milk iso lates. It was concluded that the relatively high counts of toxigenic E . coli in bulk milk originating from dairy farms in Trinidad could pos e a health risk to consumers. The poor microbial quality of water used on farms may be an important source of contamination of milk.