pilus

1. [TA] SYN: hair (1). 2. A fine filamentous appendage, somewhat analogous to the flagelium, that occurs on some bacteria. Pili consist only of protein and are shorter, straighter, and much more numerous and may be chemically similar to flagella; specialized pili (F pili, I pili, and other conjugative pili) seem to mediate bacterial conjugation. SYN: fimbria (2). SEE ALSO: conjugative plasmid. [L.]

- pili annulati SYN: ringed hair.

- F pili p. (2).

- F p. a structure responsible for attachment of individual male (F⁺) to female (F⁻) bacteria, forming conjugal pairs.

- I pili p. (2).

- pili multigemini the presence of several hairs in a single follicle.

- R pili specialized pili found on bacterial cells, similar to F pili and associated with R plasmids.

- pili torti a condition in which many hair shafts are twisted on the long axis, congenital or acquired as a result of distortion of the follicles from a scarring inflammatory process, mechanical stress, or cicatrizing alopecia; the hair shafts resemble spangles in reflected light, are brittle, and break at varying lengths with many areas appearing bald with a dark stubble; as a developmental defect it can be manifested in such syndromes as Bjornstad, Crandall, and Menkes. SYN: twisted hairs.

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pi·lus 'pī-ləs n, pl pi·li -.lī a hair or a structure (as on the surface of a bacterial cell) resembling a hair

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n.

a hair. See also pili.

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pi·lus (piґləs) gen. and pl. piґli [L.] 1. hair. 2. in microbiology, one of the minute filamentous appendages of certain bacteria; they are considerably smaller and less rigid than flagella and are associated with antigenic properties and sex functions of the cell; called also fimbria.