Escherichia coli colonization factor antigen CS5 (CS5)

Escherichia coli colonization factor antigen CS5 (“CS5”) is a proteinaceous, fibrillar surface structure (pilus/fimbria) on enterotoxigenic Escherichia coli (ETEC), which acts as a key *virulence factor* enabling the bacteria to adhere specifically to the epithelium of the human small intestine[1][2][4]. The CS5 pilus is encoded by the csf operon, consisting of several genes (csfA, csfB, csfC, csfD, csfE, csfF) that together mediate the biosynthesis, assembly, and expression of functional pili[1][2][3][4]. These pili initiate ETEC colonization, which is the first step before toxin-mediated diarrheal disease. CS5 is typically co-expressed with another colonization factor, CS6, in many clinically relevant ETEC strains[4]. Its expression is tightly regulated and can be robustly induced by bile salts—particularly sodium glycocholate—as found in the gut[4]. The major subunit of the pilus, encoded by csfA, is homologous to analogous subunits in other bacterial fimbriae (e.g., F41). The CS5 pilus is classified as part of CFA/IV group in ETEC virulence antigens and is a major target for preventive strategies such as vaccine development[1][2][4]. **Note:** No direct drugs or vaccines specifically targeting CS5 are currently approved, but it is under investigation as a candidate for ETEC vaccine development due to its role in pathogenesis[1][4]. CS5 is not a human receptor or enzyme but is considered a validated pathogenic bacterial target.

Other names

Coli surface antigen 5CFA/IV CS5 pilusCS5 fimbriaeColonization factor antigen CS5