Identification of infant and adult swine susceptible to enterotoxigenic Escherichia coli by detection of receptors for F4(K88)ac fimbriae in brush borders or feces.

We attempted to determine F4(K88)-adhesive and non-adhesive phenotypes of infant (neonatal < 3 day old and weaned < 4 week old pigs) and adult (> 6 month old) swine by ELISA using immobilized F4(K88)ac fimbrial antigen or whole F4(K88) + E. coli cells (strains M1823 and 1476) and isolated small intestinal brush borders or easily-obtainable fecal samples from the same animals. Nineteen of 22 neonates (86%), 17 of 20 weaners (85%), and 26 of 39 adults (67%) were classified identically as F4(K88) receptor-positive or negative by the ELISA. The ELISA with feces from adult swine was found to be almost equally specific (87%) as that with feces from neonatal (90%) and weaned (91%) pigs. However, the sensitivity of the assay was low (38%), indicating that fecal samples from adults contained less receptor-material than necessary for comparable phenotyping. The receptor-positive brush borders from neonates and weaners reacted significantly better (P < 0.02, < 0.001 respectively) with purified F4(K88) antigen than did those from adults. There was good agreement between the average ELISA values for feces from infant and adult swine regardless the source of coating antigen applied. With this assay we can determine F4(K88) phenotypes of infant swine using easily-collected fecal samples rather than isolated brush borders. It was also concluded that tested feces is not an acceptable alternate source of the receptor-material to brush borders from F4(K88)-susceptible adult swine.