This included isolates belonging to serotype O8 that produced heat-stable and heat-labile enterotoxins but did not produce any of the recognized fimbriae (F4, F5, F6, F41, F18).
In vitro hemagglutination (unique mannose-resistant hemagglutination activity with guinea pig, sheep, human, and chicken red blood cells at 37°C, but not at 18°C) and enterocyte brush border attachment assays suggested that the F– ETEC strains produced an unidentified colonization factor that promoted adherence to the intestinal epithelium.
Colostrum-deprived 1-day-old piglets challenged with an F– strain (1–2 x 109 bacteria) developed acute watery diarrhea within 4 hours of inoculation and suffered up to 20% weight loss, with comparable severity to piglets challenged with conventional F4 and F5 strains.
At necropsy, viable counts and histopathologic examination of intestinal sections demonstrated colonization of the duodenum, jejunum, and ileum by F4-positive strains.
In comparison, the F– and F5-positive strains attached exclusively to the ileum. Transmission electron micrographs of negatively stained F– cells grown at 37°C demonstrated the presence of fimbriae.
These results confirm the presence of a potentially new pathogenic ETEC fimbrial type in piggeries in Vietnam, with a unique hemagglutination property and attachment characteristics similar to ETEC bearing F5 fimbriae.
Source: T. N. Do, I. Wilkie, S. J. Driesen, V. A. Fahy and D. J. Trott (2006): Pathogenicity of Vietnamese Enterotoxigenic Escherichia coli Strains in Colostrum-deprived One-day-old Piglets. In: Vet Pathol 43:150-160 (2006)
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