Fimbriae, Pili

 Fimbriae

· Short, fine, hair like appendages thinner than flagella and not involved in motility - a cell may be covered with up to 1,000 fimbriae - Only visible in an electron microscope

· Slender tubes composed of helically arranged fimbrillin protein subunits - 3 to 10 nm in diameter & several μm long 

· Attach bacteria to solid surfaces such as rocks in streams and host tissues

Pili

· Sex pili - about 1 to 10 per cell- often are larger than fimbriae (around 9 to 10 nm in diameter) - made of pilin protein subunits

· Genetically determined by sex factors or conjugative plasmids; required for bacterial mating

· Some bacterial viruses attach specifically to receptors on sex pili at the start of their reproductive cycle.

Fimbriae	Pili
Fimbriae are tiny bristle-like fibers arising from the surface of bacterial cells.	Pili are hair like microfibers that are thick tubular structure made up of pilin.
Shorter than pili	Longer than fimbriae.
Thin	Thicker than fimbriae.
200-400 per cell	less 1-10 per cell
Fimbrillin protein	Pilin protein
Less rigid	More rigid than fimbriae
Both gram positive and gram negative bacteria	Only gram negative bacteria
Is governed by bacterial genes in the nucleoid region	Is governed by plasmid genes.
Responsible for cell to surface attachment. Specialized for attachment i.e. enable the cell to adhere the surfaces of other bacteria.	Responsible for bacterial conjugation. Two basic function of pili. They are gene transfer and attachment.
Do not function in active motility	Type IV pili shows twitching type of motility.
No receptors of other	Serve as receptor for certain viruses
Salmonella typhimurium, Shigella dysenteriae.	Escherichia coli, Neisseria gonorrhoeae.
Shigella dysenteriae uses its fimbriae to attach to the intestine and then produces a toxin that causes diarrhea.	Neisseria gonorrhoeae, the cause of gonorrhea, uses pili to attach to the urogenital and cervical epithelium when it causes disease.