**6. Pili and type I fimbriae**

The type IV pili are best characterized, which are composed of the Pil A subunit in a form of a helical polymer. Hahn and Solow reported that these IV pili are localized to the poles of the bacterial cells and facilitate the adhesive properties of *P. aeruginosa* [25]. Type IV pili appear to be required for biofilm formation and host colonization. Cell aggregation and formation of microcolonies are promoted by Type IV pili [26, 27]. *P. aeruginosa* having three sets of type I fimbriae (*CupA, CupB* and *CupC* fimbriae) which assembled by the chaperone usher pathway. CupA fimbriae demonstrated as important for adherence to abiotic surfaces causing biofilm formation and auto-aggregation of small colony variants (SCV) in *P. aeruginosa* [28].
