Submitted to: Rushmore Conference on Mechanisms in Pathogenesis of Enteric Diseases
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/1998
Publication Date: N/A
Technical Abstract: Cattle are an important reservoir of Shiga toxin-producing Escherichia coli O157:H7 and other enterohemorrhagic E. coli (EHEC) that cause diarrhea, hemorrhagic colitis, and hemorrhagic uremic syndrome in humans. One strategy for reducing human foodborne EHEC infections is to reduce levels of EHEC in cattle. We are using bovine O157:H7 infection models to identify EHEC virulence factors that promote colonization and fecal shedding in bovines. EHEC O157:H7 cause severe diarrhea and attaching and effacing (A/E) mucosal lesions in colostrum-deprived neonatal (<12 h) calves. A/E bacteria are consistently found in tissues with >/= 10**6 CFU of O157:H7/g of tissue. We hypothesized that EHEC O157:H7 also cause A/E lesions in older calves, but these were not detected in earlier studies because intestinal levels of O157:H7 were too low at necropsy. Weaned 3- to 4-month-old calves were fasted 48 h, inoculated via stomach tube with 10**10 CFU of EHEC O157:H7 or nonpathogenic E. coli, necropsied 2 to 14 d pi and examined histologically. All calves inoculated with O157:H7 remained clinically normal and had higher levels of inoculated E. coli than control animals. Some O157-infected calves, but no controls, had A/E bacteria in the rectum (3 of 9 calves) and cecum (2 of 7 calves), but only in tissues with >10**5.5 CFU of O157:H7/g of tissue. The rectum was the major site of colonization. Weaned calves, like neonatal calves, are susceptible to intestinal damage induced by E. coli O157:H7. The rectum and cecum may be the principal sites of E. coli O157:H7 colonization during the carrier-shedder state in cattle.