Role of the K88 antigen in the pathogenesis of neonatal diarrhea caused by Escherichia coli in piglets.

The role of the K88 antigen of Escherichia coli in neonatal diarrhea of piglets was studied by comparing a K88-positive strain with three K88-negative strains derived from the K88-positive strain. K88 antigen was produced by the K88-positive strain in the intestinal tract of gnotobiotic piglets, whereas K88-negative strains did not regain the ability to synthesize K88 antigen. Synthesis of the antigen conferred different colonization characteristics on the four strains; K88-positive bacteria adhered to the mucosa of the small intestine, whereas K88-negative bacteria did not attach and were distributed throughout the lumen. Adhesion of K88-positive bacteria to tissue from the small intestine of gnotobiotic piglets was demonstrated in vitro and was inhibited by antisera that contained K88 antibodies. Attachment did not occur with bacteria grown at 18 C. Adhesion of cell-free K88 antigen was also demonstrated. The K88-positive strain and one of the K88-negative strains were equally virulent in gnotobiotic piglets. In contrast, the K88-positive strain killed 50% of conventionally reared piglets, whereas the K88-negative strain killed only 3%. Adhesion of the K88-positive strain, but not of the K88-negative strain, to the mucosa of the small intestine was demonstrated. Our results show that K88 antigen is responsible for attachment of K88-positive bacteria to the wall of the small intestine, and that adhesion is essential for the virulence of K88-positive bacteria in conventionally reared piglets.