Let me share with you a comparison between pilli and flagella of bacteria.
| Aspect | Pili | Flagella |
| Structure | Short, hair-like appendages made of proteins | Long, whip-like appendages made of proteins |
| Composition of Filament | Typically rigid and composed of a helical arrangement of pilin subunits | Flexible and helical, composed of flagellin subunits |
| Functions
| · Pili facilitate adhesion to surfaces, allowing bacteria to attach to host cells or environmental substrates. · Sex or F (fertility) pili are involved in bacterial conjugation. | · Primary function of flagella is to help in motility, allowing bacteria to swim through liquid environments or move along surfaces. |
| Number | Multiple pili may be present on a single bacterial cell | Generally, a bacterium possesses a few to several flagella |
| Length | Shorter as compared to flagella | Longer compared to pili |
| Attachment | Pili are shorter and more numerous, providing a velcro-like effect for adhesion | Flagella are longer and provide a propeller-like motion for bacterial movement |
| Variants | · Common pili involved in adhesion · Sex pili involved in conjugation | · Polar flagella (at one or both ends) · Peritrichous flagella (distributed over the entire surface) |
| Role in Pathogenesis | Pili play a role in bacterial colonization and pathogenesis by promoting adhesion to host tissues | Flagella contribute to bacterial pathogenesis by enabling movement toward or away from host cells and tissues |