A
pilus (
Latin for 'hair'; plural :
pili) is a hairlike appendage found on the surface of many
bacteria. The terms
pilus and
fimbria (Latin for 'fringe'; plural:
fimbriae) can be used interchangeably, although some researchers reserve the term
pilus for the appendage required for
bacterial conjugation. All pili are primarily composed of
oligomeric pilin proteins.