A comparison of histopathological changes in calves associated with K99- and K99+ strains of enterotoxigenic Escherichia coli.

Enterotoxigenic colibacillosis was experimentally produced in four colostrum-deprived calves given 10(10) Escherichia coli strain 210 (serotype 09+:K30+:K99-:F41-:H-) orally and the histopathological changes compared to those seen in colostrum-fed calves infected in an earlier study with strain B44 (serotype 09+:K30+:K99+:F41+:H-). Escherichia coli strain 210 caused diarrhea, atrophic villi with cuboidal epithelium, and focal accumulations of a few neutrophils in the dome villi above Peyer's patches but neither the clinical nor the histopathological changes were as pronounced as with strain B44. The extent and distribution of adherence to the mucosal surface differed between the two strains. Strain B44 adhered as a continuous layer over most of the absorptive epithelial surface of both the jejunum and ileum. Adherence of strain 210 was restricted to the ileum and the bacteria often adhered focally in "clumps" rather than as a continuous layer, especially on the distal half of the villous surface.