Virulence properties of enterotoxigenic Escherichia coli O8: KX105 strains isolated from diarrheic piglets.

Twenty-two enterotoxigenic Escherichia coli (ETEC) O8:KX105 strains isolated from 1- to 7-week-old diarrheic piglets were examined for virulence properties. Thirteen strains caused acute watery diarrhea in orally infected, colostrum-deprived newborn piglets, whereas the remaining nine did not. The enteropathogenic strains colonized the small intestine, albeit with lower intensity than classical porcine ETEC. They produced the heat-stable STb and heat-labile LT enterotoxins, whereas the nonenteropathogenic strains produced the STb enterotoxin alone. None of the E. coli O8:KX105 strains exhibited mannose-resistant hemagglutination with erythrocytes from 12 species. Ten of the enteropathogenic and two of the nonenteropathogenic strains were positive for mannose-sensitive hemagglutination. These strains produced rodlike fimbriae 3 to 5 nm in diameter, whereas no fimbriae were detected on the other strains. None of the 22 strains produced the fimbrial antigens F4, F5, F41, F2, F3, FY(Att 25), and F165. Of the 13 enteropathogenic strains, 10 expressed the F6 antigen in the intestines of infected piglets but not in cultures. The other three enteropathogenic strains apparently lacked all of the known fimbrial antigens from porcine ETEC.