Type IV pili, filamentous surface appendages primarily composed of a single protein subunit termed pilin, play a crucial role in the initiation of disease by a wide range of pathogenic bacteria. Although previous electron microscopic studies suggested that pili might be present on the surface of Moraxella catarrhalis isolates, detailed molecular and phenotypic analyses of these structures have not been reported to date. We identified and cloned the M. catarrhalis genes encoding PilA, the major pilin subunit, PilQ, the outer membrane secretin through which the pilus filament is extruded, and PilT, the NTPase that mediates pilin disassembly and retraction. To initiate investigation of the role of this surface organelle in pathogenesis, isogenic pilA, pilT, and pilQ mutants were constructed in M. catarrhalis strain 7169. Comparative analyses of the wild-type 7169 strain and three isogenic pil mutants demonstrated that M. catarrhalis expresses type IV pili that are essential for natural genetic transformation. Our studies suggest type IV pilus production by M. catarrhalis is constitutive and ubiquitous, although pilin expression was demonstrated to be iron responsive and Fur regulated. These data indicate that additional studies aimed at elucidating the prevalence and role of type IV pili in the pathogenesis and host response to M. catarrhalis infections are warranted.Moraxella catarrhalis is now recognized as an important human pathogen in both children and adults (12,16,19,33,49). This organism is a significant cause of otitis media and sinusitis in young children and also causes lower respiratory tract disease in adults, particularly those with chronic lung disease (12,33,34). In addition, a few reports have described nosocomial spread of this bacterium in respiratory wards (6-9, 35). The extremely high carriage rates reported in children, coupled with the fact that over 90% of M. catarrhalis clinical isolates are ␤-lactamase positive, suggest that infections with these organisms may increase (12,48). Multiple studies, including those from our laboratory, have described specific bacterial components as potential virulence factors (for a recent review, refer to reference 49). Although little information is available regarding the actual steps involved in the pathogenesis of M. catarrhalis infections, it is clear that these organisms must attach to the human mucosal surface in order to establish colonization. Therefore, the identification of bacterial colonization factors and of new vaccine and treatment targets is a major focus of present research efforts. In this study, we describe the identification and characterization of the genes that are involved in the biosynthesis and assembly of M. catarrhalis pili.Pili are homo-or heteropolymers composed of helically arranged subunits assembled and expressed on the surface of a broad spectrum of gram-negative bacteria and can be classified based on morphology and function.

No abstract