Many Gram-negative bacteria possess thin microfibrils made of proteins (0.11.5 nm thick, 4-8 nm long), the attachment pili. They are anchored in the outer membrane of the cell wall and extend radially from the surface. Using these structures, bacteria are capable of specific attachment to host cell receptors (ligand—receptor, key—keyhole).
The conjugation pili (syn. sex pili) in Gram-negative bacteria are required for the process of conjugation and thus for transfer of conjugative plasmids (see p. 175).
Examples of Attachment Pili in Gram-Negative Bacteria
PAP (syn. P pili) Pyelonephritis-associated pili. Bind to receptors of the uro-epithelium and to the P blood group antigen (hence "P" pili). The specific receptors for these pili are plentiful on the uro-epithelial surface. PAP are characteristic of the uropathological variety of Escherichia coli that causes spontaneous urinary tract infections in patients showing no tract obstruction.
CFA1, CFA2 Colonization factors. Pili responsible for specific binding of en-teropathogenic coli bacteria to enterocytes.
Gonococcal Used for specific attachment of gonococci mucosal cells of the attachment pili urogenital epithelium.
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