Pathogenesis of O157:H7 Escherichia coli infection in neonatal calves.

Cattle have been implicated as an important reservoir of Shiga-like toxin-producing Escherichia coli (SLTEC) O157:H7, enterohemorrhagic E. coli (EHEC) that cause hemorrhagic colitis and hemorrhagic uremic syndrome in humans. Naturally- or experimentally-infected cattle can shed low levels of E. coli O157:H7 long-term, but little is known about the pathogenesis of E. coli O157:H7 infection in cattle. E. coli O157:H7 induce characteristic attaching and effacing (A/E) mucosal lesions in ceca and colons of 1-day-old gnotobiotic piglets and this model is used to study the pathogenesis of SLTEC infections. A/E lesions were not detected in histologic sections of the intestines from adult cattle or 3- to 14-week-old calves infected with E. coli O157:H7. Our objective was to determine if E. coli O157:H7 induce A/E lesions in neonatal calves. Colostrum-deprived calves (< 12-h-old) were bottle-fed with antibiotic-free milk replacer containing 10(10) colony forming units (CFU) of O157:H7 (SLT-I+, SLT-II+) or nonpathogenic E. coli, necropsied 18 h postinfection and their intestines examined histologically. Bacterial attachment, effacement of microvillous borders, and destruction of epithelium were observed in the intestines of the neonatal calves inoculated with E. coli O157:H7. No lesions were observed in calves inoculated with nonpathogenic E. coli. The distribution of intestinal lesions in neonatal calves resembled that in gnotobiotic pigs. Neonatal calves are apparently more susceptible to A/E lesions induced by E. coli O157:H7 than are older calves or adult cattle and provide a model for studying the pathogenesis of E. coli O157:H7 infections in cattle.