Persistent colonization of sheep by Escherichia coli O157 : H7 and other E-coli pathotypes

Shiga toxin-producing Escherichia call (STEC) is an important cause of food -borne illness in humans. Ruminants appear to be more frequently colonized by STEC than are other animals, but the reason(s) for this is unknown. We c ompared the frequency, magnitude, duration, and transmissibility of coloniz ation of sheep by E. coli O157:H7 to that by other pathotypes of E. coli. Y oung adult sheep were simultaneously inoculated with a cocktail consisting of two strains of E. coli O157:H7, two strains of enterotoxigenic E. coli ( ETEC), and one strain of enteropathogenic E. coli. Both STEC strains and ET EC 2011 were given at either 10(7) or 10(10) CFU/strain/animal. The other s trains were given only at 10(10) CFU/strain. We found no consistent differe nces among pathotypes in the frequency, magnitude, and transmissibility of colonization. However, the STEC strains tended to persist to 2 weeks and 2 months pastinoculation more frequently than did the other pathotypes. The t endency for persistence of the STEC strains was apparent following; an inoc ulation dose of either 10(7) CFU. One of the ETEC strains also persisted wh en inoculated at 10(10) CFU. However, in contrast to the STEC strains, it d id not persist when inoculated at 10(7) CFU. These results support the hypo thesis that STEC is better adapted to persist in the alimentary tracts of s heep than are other pathotypes off. coli.