A pilus ( Latin for 'hair';plural : pili ) is a hairlike appendage found on the surfaceof many bacteria .  The terms pilus and fimbria (Latinfor 'fringe'…; plural: fimbriae ) can be used interchangeably,although some researchers reserve the term pilus for theappendage required for bacterial conjugation . All piliare primarily composed of oligomeric pilin proteins. .
Dozens of these structures can exist on the bacteria. Somebacterial viruses or bacteriophages attach to receptors on pili at the startof their reproductive cycle. .
Pili are antigenic . They are also fragile andconstantly replaced, sometimes with pili of different composition,resulting in altered antigenicity. Specific host responses to oldpili structure are not effective on the new structure.Recombination genes of pili code for variable (V) and constant (C)regions of the pili (similar to immunoglobulin diversity).Answer thisquestionâ¦ ( Full Answer )