The K99 Adherence System in Cattle
Both K88 and K99 are plasmid-mediated pilus antigens which contribute to the virulence of enterotoxigenic Escherichia coli (ETEC). The K99 adherence system differs from the K88 adherence system in some respects. K88 antigens contain an antigenically constant component and a variable component. Diarrheal disease due to infection with K88+ ETEC is confined to certain genotypes of swine. Pigs are susceptible to ETEC-induced diarrhea during the immediate neonatal period and again after weaning when they are several weeks old. Factors other than colostrum and microflora must also contribute to the development of resistance of calves and lambs to intestinal colonization by K99+ ETEC. There are several host range differences in adhesion or colonization by K88+ and K99 + ETEC. K88+ strains tend to be restricted to specific genotypes in one species, to intensively colonize the entire small intestine, and to affect individuals up to several weeks old.