Fimbria (bacteriology)


In bacteriology, a fimbria, also referred to as an "attachment pilus" by some scientists, is a type of appendage that is found on many Gram-negative and some Gram-positive bacteria, and that is thinner and shorter than a flagellum. This appendage ranges from 3–10 nanometers in diameter and can be as much as several micrometers long. Fimbriae are used by bacteria to adhere to one another and to adhere to animal cells and some inanimate objects. A bacterium can have as many as 1,000 fimbriae. Fimbriae are only visible with the use of an electron microscope. They may be straight or flexible.
Fimbriae include adhesins which attach them to some sort of substratum so that the bacteria can withstand shear forces and obtain nutrients. For example, E. coli uses them to attach to mannose receptors.
Some aerobic bacteria form a very thin layer at the surface of a broth culture. This layer, termed a, consists of many aerobic bacteria that adhere to the surface by their fimbriae. Thus, fimbriae allow the aerobic bacteria to remain both on the broth, from which they take nutrients, and near the air.
"Gram-negative bacteria assemble functional amyloid surface fibers termed curli." Curli are a type of fimbriae; another type are called type I fimbriae. Curli are composed of proteins called curlins. Some of the genes involved are CsgA, CsgB, CsgC, CsgD, CsgE, CsgF, and CsgG.

Virulence

Fimbriae are one of the primary mechanisms of virulence for E. coli, Bordetella pertussis, Staphylococcus and Streptococcus bacteria. Their presence greatly enhances the bacteria's ability to attach to the host and cause disease.