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Classification of Fimbriae / Pili

	Classification of Fimbriae / Pili - Ottow (1975) has classified fimbriae into six groups. Group I includes fimbriae which function as adhesive organelles. They range from 100-300 per organism and are peritrichously arranged. Their production is determined by the chromosome. Group I fimbriae are divided into four subtypes. Group 2 includes the sex pili. These are specia1ized filamentous appendages determined by sex factors or other extrachromosomal episomes. They include the F-pili. Group 2 pili are comparatively scarce, ranging from one to JO per organism.
They are usually longer and wider than fimbriae. They may have a distinct axial canal and may sometimes end in a terminal knob. Group 3 includes the thick, hollow tubes of Agrobacterium, which may be up to 3μm long and 400A-600A wide. Their function is not understood. Group 4 includes flexible, rod like and polarly inserted fimbriae found in Pseudomonas and Vibrio. Their function is to promote bacterial motion. Group 5 include the polarly arranged, contractile tubules found in/Pseudomonas 'rhodos', Rhizobium lupini and Agrobacterium species.
They promote conjugation of competent cells by contracting and pulling bacteria together into clusters. Group 6 fimbriae have been found in the gram positive Corynebacterium renale, which has characteristic bundles of fimbriae. Each filament has a diameter of 25-30A. The filaments act as specific antigens

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