Comparison of receptors for 987P pili of enterotoxigenic Escherichia coli in the small intestines of neonatal and older pig.

Enterotoxigenic Escherichia coli isolates that express 987P pili colonize the small intestine and cause diarrhea in neonatal (less than 6-day-old) but not in older (greater than 3-week-old) pigs. However, 987P+ E. coli isolates adhere in vitro to small-intestinal epithelial cells from pigs of both ages. This indicates that older pigs as well as neonatal pigs contain receptors for 987P pili and that resistance in older pigs is not due to a lack of intestinal receptors for 987P pili. In this study, we demonstrated that 3-week-old gnotobiotic pigs, like neonatal pigs, were colonized and developed diarrhea when challenged with 987P+ E. coli. We compared 987P receptors in small-intestinal epithelial cell brush borders and in intestinal washes (luminal contents) from less than 1-day-old, 3-week-old gnotobiotic, and 3- to 4-week-old weaned pigs. Samples were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and blotted onto nitrocellulose filters, and 987P binding was demonstrated by immunoassay using purified 987P pili. Multiple 987P-binding components ranging from 33 to 40 kDa were found in brush borders from both 987P-susceptible (neonatal and gnotobiotic) and 987P-resistant (older) pigs: 987P binding to these receptors, which we called 987R, did not correlate with 987P susceptibility. A less than 17-kDa 987P receptor, 987M, was found in the mucus fraction of intestinal washes from 987P-resistant older pigs. Only trace amounts of 987M were detected in 987P-susceptible neonatal and gnotobiotic pigs. 987M comigrated with the 987P receptor previously isolated from adult rabbits. Receptors for 987P in the mucus of older pigs may inhibit 987P-mediated intestinal colonization by preventing the attachment of 987P+ enterotoxigenic E. coli to intestinal epithelial receptors for 987P.