U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
10-2008
Citation
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 74(20): Oct. 2008, p. 6378–6384; doi:10.1128/AEM.00636-08
Abstract
Weaned 3- to 4-month-old calves were fasted for 48 h, inoculated with 1010 CFU of Shiga toxin-positive Escherichia coli (STEC) 0157:H7 strain 86-24 (STEC 0157) or STEC 091:H21 strain B2F1 (STEC 091), Shiga toxin-negative E. coli 0157:H7 strain 87-23 (Stx- 0157), or a nonpathogenic control E. coli strain, necropsied 4 days postinoculation, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of, and 1 day after inoculation). STEC 0157 bacteria were recovered from feces, intestines, or gall bladders of 74% (40/55) of calves 4 days after they were inoculated with STEC 0157. Colon and cecum were sites from which inoculum-type bacteria were most often recovered. Histologic lesions of attaching-and-effacing A/E 0157+ bacteria were observed in 69% (38/55) of the STEC 0157-inoculated calves. Rectum, ileocecal valve, and distal colon were sites most likely to contain A/E 0157+ bacteria. Fecal and intestinal levels of STEC 0157 bacteria were significantly higher and A/E 0157+bacteria were more common in DEX-treated calves than in nontreated calves inoculated with STEC 0157. Fecal STEC 0157 levels were significantly higher than Stx- 0157, STEC 091, or control, or control E. coli; only STEC 0157 cells were recovered from tissues. Identifying the rectum, ileocecal valve, and distal colon as early STEC 0157 colonization sites and finding that DEX treatment enhances the susceptibility of weaned calves to STEC 0157 colonization will facilitate the identification and evaluation of interventions aimed at reducing STEC 0157 infection in cattle.