Paper I — 2017 August (Supplementary) (2010 Scheme) — Q8
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Paper I
2017 August (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Fimbriae
Q82 marksShort Notes
Answer
Fimbriae (pili) are short, thin, straight, hair-like proteinaceous surface appendages present in large numbers (hundreds) on the surface of many Gram-negative (and some Gram-positive) bacteria — distinct from flagella, since they are not organs of motility but function primarily in adherence.
Structure: composed of repeating subunits of the protein pilin, arranged helically to form a rigid, non-motile filament, anchored to the cell envelope by a basal body.
Types:
Common (adhesive/somatic) fimbriae — mediate attachment of the bacterium to host epithelial cell surfaces or other substrates, a key initial step in colonization and infection (e.g., P-fimbriae of uropathogenic E. coli bind uroepithelium, an important virulence factor in pyelonephritis; type 1 fimbriae mediate mannose-sensitive adhesion).
Sex pilus (F pilus) — a longer, specialized structure (usually one or a few per cell), encoded by the F (fertility) plasmid, that mediates attachment between a donor and recipient bacterium during conjugation, forming the conduit through which plasmid DNA is transferred.
Clinical/biological significance: fimbrial adhesins are important virulence factors, determining tissue tropism (which host cell types/sites a bacterium can colonize) and are a first step required for many infections (e.g., colonization by enterotoxigenic E. coli, gonococcal attachment to urogenital epithelium via type IV pili, which also permit twitching motility and are subject to antigenic/phase variation to evade host immunity); fimbrial antigens are being investigated as vaccine targets in some pathogens.
