Fimbriae, Transmembrane Signaling, and Cell Activation

Attachment to mucosal surfaces enables commensal organisms to select their ecologic niche and pathogens to select their site of infection. The tissue-specific attachment involves the coupling of microbial surface adhesins to receptor epitopes on host cell surfaces and may occur in competition with soluble receptor molecules. Gram-negative bacteria carry fimbriae with lectinlike domains that recognize receptor epitopes in cell surface glycolipids or glycoproteins. The resulting specific adherence may enhance bacterial persistence at the site of infection, but adherence also has been identified as a virulence factor that facilitates tissue attack, invasion, and mucosal inflammation. Two general mechanisms have been proposed to explain how attachment promotes tissue attack by pathogenic bacteria. In the first case, the coupling of fimbriae to their receptors activates receptor-determined signaling pathways in the host cell