Enterotoxigenic K99+ Escherichia coli attachment to host cell receptors inhibited by recombinant pili protein

Most enterotoxigenic Escherichia coli (ETEC) isolated from neonatal cattle with diarrhea (enteric colibacillosis) exhibit the colonization factor antigen, K99. The K99 pili are necessary for the bacteria to bind to a receptor, N-glycolylneuraminic acid-GM3 on the host cells in the small intestine where the bacteria multiply and secrete toxins that cause the diarrhea. When the attachment of the ETEC to host cell is inhibited, the bacteria do not accumulate sufficiently in the gut to cause disease. Since purified K99 pili block K99+ ETEC from binding to host epithelia, three recombinant K99 proteins of different sizes were developed and produced to demonstrate inhibition with in vitro competitive binding assays. The full-length recombinant protein, rK99-476 inhibited the binding of ETEC with an activity similar to that of the native purified K99, whereas the truncated recombinant K99 protein had no inhibitory activity. Thus this binding activity of rK99-476, which is specific and effective in blocking the receptors on the host cells, may be able to competitively inhibit K99+ ETEC infections in cattle.