| The objectives of this one-year study were to determine the effects of pre-harvest factors on Shiga toxin-producing Escherichia coli (STEC) prevalence in California cattle and to examine the pathogenic potential and toxin production capabilities of the recovered isolates. Testing fecal samples from four feedlots (n = 642), four cow-calf operations on irrigated pastures (n = 638), six range cattle ranches (n = 774), and four dairy farms (n = 1,268) revealed STEC prevalence ranging from 0 to 4.3, 1.9 to 5.0, 0.7 to 18.6, and 0.8 to 3.2%, respectively. Several effects on STEC prevalence were found for various management practices, dietary factors, and animal factors. A total of 21 isolates belonging to 14 STEC serotypes were detected in feedlots. Of these, four are known to cause hemolytic uremic syndrome (HUS) or other human illnesses and six have not been reported previously in cattle. In cow/calf operations utilizing irrigated pastures, 30 isolates belonging to 13 STEC serotypes were detected. Of these, nine are known to cause HUS or other human illnesses and eight have not been reported previously in cattle. In cow/calf operations utilizing open range grazing, 77 isolates belonging to 35 STEC serotypes were detected. Of these, 13 are known to cause HUS or other human illnesses and 21 have not been reported previously in cattle. In dairy farms, 33 isolates belonging to 16 STEC serotypes were detected. Of these, four are known to cause HUS or other human illnesses and 10 have not been reported previously in cattle. Because our STEC isolates produced one or more of the virulence factors studied (stx1, stx 2, hlyA, EHEC-hlyA, and/or adhesion of some kind), their pathogenic potential to humans should not be ignored. |
