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As the primary antigenic determinants, virulence factors and impunity factors on the cell surface of a number of species of gram-negative and some gram-positive bacteria, including Enterobacteriaceae, Pseudomonadaceae, and Neisseriaceae, there has been much interest in the study of pili as an organelle of adhesion and as a vaccine component.
Although not all bacteria have pili or fimbriae, bacterial pathogens often use their fimbriae to attach to host cells. In Gram-negative bacteria, where pili are more common, individual pilin molecules are linked by noncovalent protein-protein interactions, while Gram-positive bacteria often have polymerized LPXTG pilin. [1]
Chaperone-usher fimbriae (CU) are linear, unbranching, outer-membrane pili secreted by gram-negative bacteria through the chaperone-usher system rather than through type IV secretion or extracellular nucleation systems.
Neisseria meningitidis, often referred to as the meningococcus, is a Gram-negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. The bacterium is referred to as a coccus because it is round, and more specifically a diplococcus because of its tendency to form pairs.
Haemophilus ducreyi is a Gram-negative coccobacillus, and has a shape between a spherical coccus [6] and a rod-shaped bacterium. [1] This species of bacterium has pili, fine and tangled appendages composed predominantly of protein, that allow bacteria to attach to surfaces, including those of cells. [7]
Twitching motility is a form of crawling bacterial motility used to move over surfaces. Twitching is mediated by the activity of hair-like filaments called type IV pili which extend from the cell's exterior, bind to surrounding solid substrates, and retract, pulling the cell forwards in a manner similar to the action of a grappling hook.
A Gram stain of a urethral exudate showing typical intracellular Gram-negative diplococci, which is diagnostic for gonococcal urethritis [17]. Neisseria species are fastidious, Gram-negative cocci (though some species are rod-shaped and occur in pairs or short chains) that require nutrient supplementation to grow in laboratory cultures. [18]
Pili multigemini, also known as "compound hairs," [2] is a malformation characterized by the presence of bifurcated or multiple divided hair matrices and papillae, giving rise to the formation of multiple hair shafts within the individual follicles.