Ganglioside epitope recognized by K99 fimbriae from enterotoxigenic Escherichia coli.

The receptor structure recognized by Escherichia coli possessing K99 fimbriae and by isolated K99 fimbrial fractions was examined by using an equine erythrocyte hemagglutination inhibition test. Both K99-positive organisms (strain B41) and fimbrial preparations reacted with N-glycolylneuraminyl-lactosyl-ceramide (NeuGcLacCer) purified from equine erythrocytes with very high potency. Fimbrial preparations were 253 times more potent than intact organisms, indicating that isolated fimbriae more precisely recognize the structure of NeuGcLacCer than do fimbriae located on the bacterial cell wall. Structurally, the N-glycolyl group of the sialic acid was shown to be essential because substitution of the N-acetyl group for the N-glycolyl group caused the reactivity to completely disappear. The substitution of the O-acetyl group for the C4 hydroxyl group of the sialic acid (4-O-Ac-NeuGcLacCer) also diminished the reactivity by about 500 times, indicating that the fine structure of NeuGc is necessary for recognition. N-Glycolylneuraminyl-neolactotetraosyl-ceramide (NeuGcnLc4Cer) and N-glycolylneuraminyl-neolactohexaosyl-ceramide (NeuGcnLc6Cer), both of which have identical disaccharides at the nonreducing terminal and longer carbohydrate chains, showed reduced reactivity, indicating that the ceramide of NeuGcLacCer is also involved in the recognition. Indeed, NeuGcLac oligosaccharides altered by cleavage of the ceramide or the terminal sialic acid (NeuGc) showed dramatically reduced reactivities. Ten other E. coli strains (isolated from diseased calves) and two strains (isolated from diseased piglets) which possessed the same K99 antigen and various O antigens were used for the recognition test. The results obtained were similar to those mentioned above.