Fimbriae (also called pili) are polar filaments radiating from the surface of the bacterium to a length of 0.5-1.5 micrometers and numbering 100-300 per cell. They enable bacteria to colonize the epithelium of specific host organs. Flexible pili possess hemagglutinating function. Homomer. A.hydrophila possesses two distinctive pilus types: 'straight' pili appears as brittle, rod-like filaments, whereas 'flexible' pili are supple and curvilinear.