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a long, thin, straight appendage of hydrophobic protein present in large numbers, sometimes as many as several thousand, on the cell surface of gram-negative bacteria. A fimbria measures as much as 12 micrometers in length and less than 100 angstroms in width. It is much finer and shorter than a flagellum. Male bacterial cells (donors) may have one to three sex fimbriae, or pili, that attach themselves to female cells (recipients) to form hollow bridges through which DNA may be transferred during bacterial conjugation. Fimbriae may be found in both motile and nonmotile bacteria. They usually originate from the basal granule in the cytoplasmatic membrane and pass to the exterior through the cell wall. Fimbriae enable a bacterial cell to adhere indiscriminately to solid surfaces of cells and tissues.
A. A. IMSHENETSKII