Enterohemorrhagic Escherichia coli in calves: Characterization and effects of diet

Enterohemorrhagic Escherichia coli (EHEC), are foodborne human pathogens of world-wide distribution that cause hemorrhagic colitis and hemolytic uremic syndrome. Bovine feces and gastrointestinal contents have been identified as a principal foodborne source of E. coli O157:H7 and attempts are being made to reduce environmental contamination by reducing EHEC shedding by cattle. The goals of this study were to evaluate the effects of diet on rumen proliferation and fecal shedding of E. coli O157:H7 in calves, and to evaluate development of acid resistance of E. coli O157:H7 in rumen fluid from steers on different diets. An additional objective was to compare the pathogenicity and fecal shedding of the three most common EHEC serotypes in neonatal and weaned calves.; In the present studies, despite the lower concentrations of inhibitory rumen volatile fatty acids (VFAs) and lower rumen acidity, high-roughage fed calves did not have greater rumen or fecal populations of E. coli O157: H7 in comparison to calves fed high-concentrate diet. Two calves from the high-concentrate fed group shed the highest mean concentrations of E. coli O157:H7. A positive correlation between fecal shedding of E. coli O157:H7 and rumen VFA concentrations in the high-concentrate fed group indicates a possible effect of acid exposure in the rumen on survival and proliferation of E. coli O157:H7 in the more distal gastrointestinal sites.; Using an in vitro rumen fermentation system, we compared the effects of high-concentrate and high-roughage diets on proliferation and acid resistance of E. coli O157:H7. The rumen fluid from steers fed high-roughage diets supported the proliferation of E. coli O157:H7, while the acid resistance of E. coli O157:H7 was rapidly induced in the rumen fluid from high-concentrate fed steers. Therefore, acidic conditions in the rumen may enhance E. coli O157:H7 survival as it passes extreme acidic conditions of the abomasum.; In experimentally challenged neonatal and weaned calves, E. coli O157:H7, O26:H11, and O111:NM were nonpathogenic. Neonatal calves appear less likely to carry and shed E. coli O157:H7 in comparison to other two serotypes. In the weaned calves, all three serotypes had similar shedding patterns for 32–34 days. Although shed in small populations throughout the experiment, populations of E. coli O111:NM in feces were significantly smaller than populations of other two EHEC serotypes after 16 days postinoculation. Therefore, large populations of E. coli O26:H11 and O157:H7 are more likely to be carried and shed by weaned calves.