title: Experimental Escherichia coli O157:H7 carriage in calves.
abstract: Nine weaned calves (6 to 8 weeks of age) were given 10(10) CFU of a five-strain mixture of enterohemorrhagic Escherichia coli O157:H7 by oral-gastric intubation. After an initial brief period of pyrexia in three calves and transient mild diarrhea in five calves, calves were clinically normal throughout the 13- to 27-day study. The population of E. coli O157:H7 in the faces decreased dramatically in all calves during the first 2 weeks after inoculation. Thereafter, small populations of E. coli O157:H7 persisted in all calves, where they were detected intermittently in the feces and rumen contents. While withholding food increased fecal shedding of E. coli O157:H7 by 1 to 2 log10/g in three of four calves previously shedding small populations of E. coli O157:H7, the effect of fasting on fecal shedding of E. coli O157:H7 was variable in calves shedding larger populations. At necropsy, E. coli O157:H7 was not isolated from sites outside the alimentary tract. E. coli O157:H7 was isolated from the forestomach or colon of all calves at necropsy. Greater numbers of E. coli O157:H7 were present in the gastrointestinal contents than in the corresponding mucosal sections, and there was no histologic or immunohistochemical evidence of E. coli O157:H7 adhering to the mucosa. In conclusion, under these experimental conditions, E. coli O157:H7 is not pathogenic in weaned calves, and while it does not appear to colonize mucosal surfaces for extended periods, E. coli O157:H7 persists in the contents of the rumen and colon as a source for fecal shedding.
authors.affiliation: Athens Diagnostic Laboratory, University of Georgia, Athens 30602, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Brown
authors.forename: B G
authors.initials: BG
authors.lastname: Harmon
authors.forename: T
authors.initials: T
authors.lastname: Zhao
authors.forename: M P
authors.initials: MP
authors.lastname: Doyle
mesh_terms: D000818:Animals; D002417:Cattle / Q000382:microbiology*; D002418:Cattle Diseases / Q000382:microbiology / Q000473:pathology; D003611:Dairy Products / Q000382:microbiology; D004197:Disease Reservoirs; D004927:Escherichia coli Infections / Q000382:microbiology / Q000473:pathology / Q000662:veterinary; D019453:Escherichia coli O157 / Q000254:growth & development / Q000302:isolation & purification / Q000472:pathogenicity*; D005243:Feces / Q000382:microbiology; D008297:Male; D008460:Meat / Q000382:microbiology; D009928:Organ Specificity; D013997:Time Factors; D014774:Virulence