Infection of gnotobiotic calves with Escherichia coli o157:h7 strain A84.

Six colostrum-deprived, hysterotomy-derived calves were maintained under sterile conditions and fed a milk replacer diet. At five days of age, five of the calves were dosed orally with 10(9) cfu of Escherichia coli O157:H7 strain A84. They were killed after, one, two, six, 12 and 24 days, and samples were taken for bacteriological and pathological examination. The sixth uninfected control calf was killed at seven days of age and matched samples were taken for pathological comparison. The animals remained normal throughout the observation period. Bacteriological data indicated a heavy bacterial load of strain A84 throughout the gastrointestinal tract but the bacterium was not found in liver, kidney or muscle. No evidence of 'attaching and effacing' lesions in the small or large intestine was found although there was a mild inflammatory response in the intestinal tract, consisting mainly of infiltrating eosinophils.