Age-related resistance to 987P fimbria-mediated colonization correlates with specific glycolipid receptors in intestinal mucus in swine

Abstract

Strains of enterotoxigenic Escherichia coli that produce 987P fimbriae (987P+ strains) colonize the small intestines and cause diarrhea in neonatal (< 6-day-old) pigs but not in weaned pigs. However, 987P+ E. coli strains adhere in vitro to intestinal epithelial cells from pigs of both ages. Two intestinal components, designated 987R and 987M, bind 987P fimbriae (987P) on Western blots (immunoblots). We examined brush borders (BB) and intestinal washes (IW) from pigs to determine if they contain glycolipids which bind 987P. Total glycolipid extracts from BB and IW of 4-week-old pigs were separated on thin-layer chromatograms and overlaid with purified 987P. Bound 987P were detected with 987P-specific antiserum. 987P bound to at least one moiety in both BB and IW glycolipids and also bound to several purified glycolipids, including gangliotetraosylceramide, lactosylceramide (CDH), sulfatide (SFT), gangliotriaosylceramide, and galactosylceramide (listed in order of decreasing affinity). Strain 987, but not the isogenic 987P- strain I36, bound to these same glycolipids, indicating that the fimbriae contain the adhesin required for binding to these lipids. Glycolipids extracted from BB and IW isolated from 3- and 4-week-old pigs and from BB isolated from 1-day-old pigs contained similar amounts of glycolipids like CDH and SFT that bound 987P. Finally, 987P bound to CDH, SFT, and total BB glycolipids separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to Immobilon, and these glycolipids had mobilities similar to that of 987M. Thus, 987M may contain 987P-binding glycolipids. We hypothesize that glycolipid receptors for 987P, most likely CDH or SFT, in the mucus of older pigs bind 987P and inhibit 987P- mediated intestinal colonization by preventing the attachment of 987P+ E. coli to 987P receptors on the intestinal epithelium.