PATHOGENICITY OF ESCHERICHIA-COLI O157-H7 IN THE INTESTINES OF NEONATAL CALVES

Cattle are an important reservoir of Shiga toxin-producing enterohemor rhagic Escherichia coli (EHEC) O157:H7 strains, foodborne pathogens th at cause hemorrhagic colitis and hemolytic uremic syndrome in humans. EHEC O157:H7 strains are not pathogenic in cah es >3 weeks old. Our ob jective was to determine if EHEC O157:H7 strains are pathogenic in neo natal calves. Carves <36 h old inoculated with EHEC O157:H7 developed diarrhea and enterocolitis with attaching and effacing (A/E) lesions i n both the large and small intestines by 18 h postinoculation. The sev erity of diarrhea and inflammation, and also the frequency and extent of A/E lesions, increased by 3 days postinoculation. We conclude that EHEC O157:H7 strains are pathogenic in neonatal calves. The neonatal c alf model is relevant for studying the pathogenesis of EHEC O157:H7 in fections in cattle. It should also be useful for identifying ways to r educe EHEC O157:H7 infections in cattle and thus reduce the risk of EH EC O157:H7 disease in humans.