Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/14/2008
Publication Date: 10/20/2008
Citation: Nystrom, E.A., Stoffregen, W.C., Bosworth, B.T., Moon, H.W., Pohlenz, J.F. 2008. Early Attachment Sites for Shiga-toxigenic Escherichia coli O157:H7 in Experimentally Inoculated Weaned Calves. Applied and Environmental Microbiology. 74(20):6378-6384. Interpretive Summary: Cattle are an important source of Shiga toxin-producing Escherichia coli (STEC) O157:H7 bacteria, foodborne pathogens that cause severe diarrhea and sometimes kidney failure and death in humans. One way to reduce the risk of STEC O157:H7 infections in humans is to reduce the level of STEC O157:H7 in cattle. This manuscript describes early STEC O157:H7 colonization sites in experimentally-inoculated weaned calves and the effects of dexamethasone (used to simulate stress) on STEC colonization in calves. Early STEC O157:H7 colonization sites were defined as sites from which the inoculum bacteria was recovered by direct culture or sites with histologic evidence of O157-associated tissue damage in tissues at 4 days after oral inoculation with STEC O157:H7. Calves treated with dexamethasone were more susceptible to STEC O157:H7 colonization. Colon and cecum were sites from which inoculum type bacteria were most often recovered. Rectum, ileo-cecal valve and distal colon were the sites most likely to O157-associated tissue damage. Ileum and gall bladder were other sites where STEC O157:H7 were found. The identification of sites where STEC O157:H7 initially colonize in cattle will facilitate identification of bacterial and host factors that promote STEC infections in cattle. Knowing where STEC O157:H7 initially colonize in cattle is critical for evaluating strategies aimed at reducing STEC infections in cattle.
Technical Abstract: Weaned 3-to- 4-month-old calves were fasted 48 h, inoculated with 10**10 CFU of Shiga toxin-positive Escherichia coli (STEC) O157:H7 strain 86-24 (STEC O157) or STEC O91:H21 strain B2F1 (STEC O91), Shiga toxin-negative E. coli O157:H7 strain 87-23 (Stx**- O157), or non-pathogenic control E. coli, necropsied 4 d pi, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of inoculation, and 1 day after inoculation). Inoculum type bacteria were recovered from the feces, intestines, or gall bladders of 74% of the calves 4 days after they were inoculated with STEC O157. Histologic lesions of attached and effacing (A/E) O157**+ bacteria were observed in 69% of the STEC O157-inoculated calves. Treatment with dexamethasone enhanced the susceptibility of weaned calves to STEC O157 colonization. Fecal and intestinal levels of inoculum type bacteria were higher and A/E O157**+ bacteria were more common in DEX-treated calves than in non-treated calves inoculated with STEC O157. Colon and cecum were sites from which inoculum type bacteria were most often recovered. Rectum, ileo-cecal valve and distal colon were the sites most likely to contain A/E lesions. Fecal levels of STEC O157 were significantly higher than those of Stx**- O157, non-STEC O91, or control E. coli. STEC O157 was the only strain detected in the tissues at 4 days after inoculation. Fecal levels of STEC O157 were significantly higher than those of Stx**- O157, non-STEC O91, or control E. coli. STEC O157 was the only strain detected in the tissues at 4 days after inoculation.