Escherichia coli K99 pilus antigen (K99 (also F5))

The Escherichia coli K99 pilus antigen (also known as the F5 antigen) is a proteinaceous, rod-shaped surface structure found on the outer membrane of certain enterotoxigenic E. coli (ETEC) strains, especially those infecting neonate livestock. Composed of multiple subunits including a major fimbrial protein called FanC, K99 pili are critical for the adhesion of E. coli to the intestinal mucosa. This initial binding facilitates the colonization and subsequent infection, leading to diarrhea in susceptible animals. K99 functions as a major virulence factor, and vaccines or monoclonal antibodies targeting this pilus are utilized to prevent disease outbreaks in agriculture. K99 fimbriae are protein filaments 0.5–1.5 micrometers long and 8.4 nm in diameter, located on the surface of ETEC. They are a major determinant in host specificity and pathogenesis, mediating attachment to intestinal epithelial cells. K99 (F5) is structurally and functionally homologous to other E. coli fimbriae like K88. No FDA-approved human drugs target K99; therapeutic approaches are almost exclusively vaccines or antibody products used in veterinary medicine.

Other names

K99 antigenF5 antigenK99 fimbrial antigenE. coli K99 fimbriaFanC

Prevention of bacterial adhesion to host cells (by vaccination or antibody binding)