Escherichia coli F5 fimbrial adhesin (F5)

The Escherichia coli F5 fimbrial adhesin, historically known as the K99 antigen, is a filamentous surface appendage found on enterotoxigenic E. coli (ETEC) strains that primarily infect neonatal calves, lambs, and piglets (UniProt: P02971). It is a critical virulence factor that facilitates the colonization of the small intestine by binding to specific sialic acid-containing glycoconjugates, such as N-glycolylneuraminic acid (Neu5Gc)-GM3, on the host's epithelial cells (PubMed: 3025437). This attachment is the essential first step for the bacteria to colonize the gut and subsequently release enterotoxins that cause severe secretory diarrhea, a condition known as colibacillosis (Merck Veterinary Manual). Because of its vital role in pathogenesis, the F5 adhesin is a primary target for veterinary immunoprophylaxis. Therapeutic strategies include maternal vaccination to enhance the transfer of specific antibodies through colostrum and the oral administration of monoclonal antibodies to newborn animals to provide immediate passive immunity (PubMed: 1643504). These interventions effectively prevent bacterial docking and the subsequent onset of clinical disease.

Other names

K99 antigenK99 fimbriaeK99 pilusF5 adhesinFanC subunit

Neutralization of the F5 fimbrial adhesin to prevent bacterial attachment to the intestinal mucosa, thereby inhibiting colonization and the subsequent effects of enterotoxins (PubMed: 1643504).