Pilus Production, Hemagglutination, and Adhesion by Porcine Strains of Enterotoxigenic Escherichia coli Lacking K88, K99, and 987P Antigens

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Abstract
Three strains of enterotoxigenic Escherichia coli which adhered, colonized intensively, and caused disease in pig intestine, but which did not produce pili of the K88, K99, or 987P antigen types were designated 3P − ETEC. The 3P − ETEC caused mannose-resistant hemagglutination, adhered to porcine intestinal epithelial cells in vitro, and produced pili. However, most bacteria taken directly from the intestine of pigs infected with 3P − ETEC appeared to be nonpiliated. Two preparations were isolated from the 3P − ETEC. One (material A) contained pili, caused mannose-sensitive hemagglutination, and did not inhibit adhesion of whole bacteria to epithelial cells in vitro. The other (material B) had no demonstrable pili, caused mannose-resistant hemagglutination, and blocked ahesion of bacteria to epithelial cells in vitro. Antiserum against an acapsular mutant (K − ) of one 3P − ETEC strain was absorbed to remove antibodies directed against somatic (O) antigen. The absorbed antiserum agglutinated all three 3P − ETEC strains grown in the K − form at 37°C, but not when they were grown at 18°C. The absorbed antiserum blocked the hemagglutinating activity of material B, but not of material A. It also reacted (via indirect immunofluorescence) with all of the 3P − ETEC when they were grown in pig intestine. The results were interpreted to indicate that: (i) the epithelial adhesive and mannose-resistant hemagglutinating activities of the 3P − ETEC strains may be mediated by an antigen contained in material B; (ii) this antigen either is not pilus associated or is associated with pili that are not demonstrable by the methods used here; (iii) the 3P − ETEC strains produce type 1 pili which do not mediate their adhesion to intestinal epithelium of pigs.

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