Pneumococcal Infection - Virulence Factors

Virulence Factors

S. pneumoniae expresses different virulence factors on its cell surface and inside the organism. These virulence factors contribute to some of the clinical manifestations during infection with S. pneumoniae.

• Polysaccharide capsule—prevents phagocytosis by host immune cells by inhibiting C3b opsonization of the bacterial cells
• Pneumolysin (Ply)—a 53-kDa pore-forming protein that can cause lysis of host cells and activate complement
• Autolysin (LytA)—activation of this protein lyses the bacteria releasing its internal contents (i.e., pneumolysin)
• Hydrogen peroxide—causes damage to host cells (can cause apoptosis in neuronal cells during meningitis) and has bactericidal effects against competing bacteria (Haemophilus influenzae, Neisseria meningitidis, Staphylococcus aureus)
• Pili—hair-like structures that extend from the surface of many strains of S. pneumoniae. They contribute to colonization of upper respiratory tract and increase the formation of large amounts of TNF by the immune system during sepsis, raising the possibility of septic shock
• Choline binding protein A/Pneumococcal surface protein A (CbpA/PspA)—an adhesin that can interact with carbohydrates on the cell surface of pulmonary epithelial cells and can inhibit complement-mediated opsonization of pneumococci