Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/25/1998
Publication Date: N/A
Technical Abstract: Cattle are important reservoirs of enterohemorrhagic Escherichia coli (EHEC) O157:H7 and other EHEC that cause hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are sporadically and asymptomatically infected with EHEC and can shed these bacteria long term. Little is known about the pathogenesis of EHEC infections in cattle. Neonatal calves <36 h old develop diarrhea and enterocolitis and have attaching and effacing (A/E) intestinal lesions by 18 h postinoculation with O157:H7. The presence of A/E lesions correlates with high intestinal levels of EHEC bacteria. We hypothesized that O157:H7 also induce A/E lesions in older calves, but these can only be detected if the numbers of O157:H7 are sufficiently high. We inoculated 7 weaned calves with O157:H7. All were clinically normal at 4 d postinoculation. A/E lesions were found in the large intestines of 3 calves that had >10**5 CFU of EHEC O157:H7/g of intestinal tissues and feces. Calf EHEC infection models are relevant for studying the pathogenesis of EHEC infections in cattle and for identifying virulence factors associated with symptomatic (neonatal) and asymptomatic (weaned) bovine EHEC infections. We found that intimin, an adhesin of EHEC O157:H7, was required for EHEC O157:H7 pathogenicity in neonatal calves. Shiga toxin was not needed for EHEC O157:H7 pathogenicity in neonatal calves, but did promote intestinal colonization in weaned calves. Anti-intimin and anti-Shiga toxin vaccines may reduce the prevalence of EHEC O157:H7 infections in cattle and thus help reduce the risk of EHEC disease in humans.