Studies in Shiga toxin-producing Escherichia coli O157:H7 determination of factors contributing to the dissemination of Escherichia coli O157:H7 among dairy farms /

by 1974- Wetzel, Amy Noel

Shiga toxin-producing Escherichia coli (STEC) O157:H7 is an important foodborne disease worldwide, and cattle play a central role in the epidemiology of human E. coli O157:H7 infection. Cattle feces are considered the primary source from which the food supply and the environment become contaminated with this pathogen. Therefore, reduction in the frequency and magnitude of fecal E. coli O157:H7 excretion by cattle is predicted to decrease the incidence of human infection. Escherichia coli O157:H7 has been sporadically isolated from other animals, and environmental sources. However, the primary routes of dissemination of E. coli O157:H7 within and between farms remains undetermined. The hypothesis that European starlings play a role in the dissemination of E. coli O157:H7 between cattle farms was tested by determining if starlings inhabiting Ohio dairy farms are a source for E. coli O157:H7 and other foodborne pathogens, and evaluating the extent to which indistinguishable isolates of E. coli O157:H7 were shared between dairy farms located in a close geographic proximity. Cultured intestinal contents of starlings captured on Ohio dairy farms showed that starlings seasonally harbor E. coli O157:H7 (late summer 20%, winter 0%) and other STEC (62.5%). ii Stx-negative O157 isolates could be lysogenized by stx2-converting bacteriophage, indicating that these toxin-negative strains may acquire stx2. Pulsed-field gel electrophoresis analysis of E. coli O157:H7 isolates recovered during a longitudinal study of 20 dairy farms in Ohio showed E. coli O157:H7 subtypes (four indistinguishable subtypes) were disseminated with considerable frequency among farms (7 of 20) in close geographic proximity and non-bovine sources may have contributed to the transmission of this organism between farms. In summary, these data support a role of wild birds in the dissemination of E. coli O157:H7 among dairy farms, but the extent of their role in dissemination of this pathogen is yet to be determined. iii