Intestinal receptors for adhesive fimbriae of enterotoxigenic Escherichia coli (ETEC) K88 in swine - a review

Determining the structure of the intestinal receptor for enterotoxigenic Es cherichia coli (ETEC) K88 fimbriae will make it possible to develop new str ategies to prevent K88+ ETEC-induced disease in pigs. Putative K88 adhesin receptors have been identified in both intestinal brush border and mucus pr eparations as either glycoproteins or glycolipids. Proteins with sizes of 2 5, 35, 40-42, 60, and 80 kDa in the intestinal mucus and 16, 23, 35, 40-70, 74, 210, and 240 kDa in brush border membranes were reported to bind speci fically to K88ab and K88ac fimbriae. The factors accounting for these varia ble results may include the variants of K88, ages, breeds, and phenotypes o f pigs, and even the sampling sites in the small intestine. Of the reported K88 receptors, only three brush border receptors, i.e., a pair of mucin-ty pe sialoglycoproteins (210 kDa or 240 kDa), an intestinal neutral glycosphi ngolipid (IGLad), and a 74-kDa transferrin glycoprotein (GP74), have fulfil led the criteria as phenotype-specific K88 fimbrial receptors. Inhibiting t he attachment of ETEC to intestine by modifying the receptor attachment sit es has been the key for developing novel approaches to preventing ETEC-indu ced diarrhea in pigs. These include: (1) receptor analogs from a variety of biological sources, (2) an enteric protected protease, (3) chicken egg-yol k containing anti-K88 fimbrial antibodies, and (4) some Lactobacillus isola tes producing proteinaceous components or carbohydrates interacting with mu cus components. Future studies should be directed to further characterize t he carbohydrate and protein moieties of receptors recognized by the K88 adh esin variants and to identify the genes responsible for susceptibility to K 88 + infections.