Capsule reduces adherence of enterotoxigenic Escherichia coli to isolated intestinal epithelial cells of pigs.

Previous reports have demonstrated that heat-stable (A-type) capsule on piliated enterotoxigenic Escherichia coli enhances colonization of enterotoxigenic E. coli in the small intestine and enhances virulence of enterotoxigenic E. coli. In this report, four encapsulated enterotoxigenic E. coli strains and one encapsulated nonenterotoxigenic strain of E. coli and their nonencapsulated mutants were tested for adhesion to isolated intestinal epithelial cells or brush borders from neonatal pigs. The enterotoxigenic E. coli also expressed the K99 pilus antigen. The nonencapsulated mutants of the four enterotoxigenic E. coli adhered in higher numbers than did the encapsulated parental strains. Both the encapsulated and nonencapsulated forms of enterotoxigenic E. coli 431 grown at 18 degrees C (K99 production suppressed) adhered poorly to the isolated cells. The nonenterotoxigenic E. coli 1793 which does not express K99 antigen also adhered poorly in both encapsulated and nonencapsulated forms. Fab fragments of anticapsular immunoglobulin G failed to block the effect of capsule on adherence of strain 431. The results indicated that K99 was the principal mediator of in vitro adhesion of the enterotoxigenic E. coli strains and that capsule impedes the in vitro adhesion. They also suggested that the capsular enhancement of colonization by such strains in vivo probably is by some mechanism other than enhanced adhesion to epithelium.