F5 fimbrial adhesin (K99) (F5)

The F5 fimbrial adhesin, historically designated as K99, is a critical surface protein found on Enterotoxigenic Escherichia coli (ETEC) that infects neonatal calves [1]. While the term Bovine pathogenic Escherichia coli surface receptors can refer to a variety of adhesins including F41 and Intimin, F5 is the primary target for commercial veterinary interventions [2]. This protein functions as a lectin, specifically binding to N-glycolylneuraminic acid (Neu5Gc) residues on the GM3 ganglioside of the host's small intestinal epithelial cells [1][2]. This adhesion is the prerequisite step for bacterial colonization and the subsequent delivery of heat-stable enterotoxins, which cause severe secretory diarrhea (scours) and high mortality in young livestock [2]. Therapeutic and preventive strategies focus on blocking this interaction using maternal vaccination or oral administration of K99-specific antibodies [3]. Vaccines like ScourGuard or Guardian induce colostral antibodies that provide passive immunity to the calf, effectively neutralizing the F5 fimbriae and preventing bacterial attachment [2][3].

Other names

K99 pilusK99 antigenF5 pilusBovine ETEC adhesinK99 fimbriae

Inhibition of bacterial attachment to the intestinal mucosa by providing or inducing antibodies that bind to and neutralize the F5 (K99) fimbrial adhesin.