Occurrence of non-sorbitol fermenting, verocytotoxin-lacking Escherichia coli O157 on cattle farms

Escherichia coli O157 is often associated with hemorrhagic colitis and the hemolytic uremic
syndrome (HUS). The verocytotoxins are considered to be the major virulence
determinants. However, vt-negative E. coli O157 were recently isolated from patients
with HUS. Several transmission routes to humans are described, but cattle feces are the
primary source from which both the food supply and the environment become
contaminated with E. coli O157.
In a prevalence study performed on dairy, beef, mixed dairy/beef and veal farms in the
summer of 2007, vt-negative isolates were detected on 11.8% (8/68) of the positive farms.
From these eight farms, a total of 43 sorbitol-negative E. coli O157:H7 were collected. On
five farms, only strains negative for the vt genes were present whereas both vt-negative
and vt-positive strains could be detected on three other farms. Further characterization
revealed that all isolates carried the eaeA and hlyA genes. Pulsed-field gel electrophoresis
(PFGE) of all isolates resulted in nine different PFGE types and within the vt-negative
strains, four different genotypes were identified, indicating that certain genetic clones are
widespread over the cattle population.

Publication year:2009

Keywords:E. coli O157, Cattle, Verocytotoxin-negative