Colonization factor antigen I fimbria (CFA-I)

Colonization factor antigen I fimbria (CFA-I) is a filamentous surface structure expressed by enterotoxigenic Escherichia coli (ETEC). It belongs to the class of adhesive pili/fimbriae that mediate initial attachment of bacteria to human small intestinal epithelial cells—a critical first step in establishing infection and delivering toxins that cause diarrheal disease. Structurally, each pilus consists mainly of repeating CfaB subunits arranged into long helical filaments approximately 8 nm in diameter and up to several micrometers long; these filaments can adopt both helical and extended conformations depending on environmental conditions. The distal tip contains an adhesin subunit responsible for binding specific receptors on host cells. CFA-I expression enables efficient colonization under physiological conditions where peristalsis would otherwise remove non-adherent bacteria from the gut lumen. Its presence correlates strongly with pathogenicity among human-infecting ETEC strains, making it a major focus for vaccine development efforts aimed at preventing traveler’s diarrhea and childhood morbidity due to ETEC infections worldwide. Immunological studies show that humans mount antibody responses against this antigen during natural infection, supporting its relevance as both a diagnostic marker in research settings and as an immunogen in candidate vaccines.

Other names

Colonization factor antigen ICFA/I fimbriaeCFA/I piliETEC colonization factor antigen I

Vaccines or antibodies targeting CFA-I aim to: - Block bacterial adhesion to intestinal mucosa, preventing colonization and subsequent toxin-mediated diarrhea. - Induce immune responses that neutralize the fimbrial structure or its adhesive tip subunit.