Bacterial Virulence Factors

Bacteria have a number of virulence factors that may be associated with disease. They include pili (fimbriae), capsules, extracellular vesicles, lipopolysaccharides, enzymes, short-chain fatty acids, polyamines, and low-molecular— weight products such as ammonia and hydrogen sulfide.

• Pili may be important for attachment to surfaces and interaction with other bacteria in a polymicrobial infection.
• Bacteria including gram-negative black-pigmented bacteria (BPB) may have capsules that enable them to avoid or survive phagocytosis.
• Lipopolysaccharides are found on the surface of gram-negative bacteria and have numerous biologic effects when released from the cell in the form of endotoxins. Endotoxins have been associated with periapical inflammation and activation of complement.
• Enzymes are produced by bacteria that may be spreading factors for infections or proteases that neutralize immunoglobulins and complement components.
• Gram-negative bacteria produce extracellular vesicles. These vesicles may contain enzymes or other toxic chemicals. It is believed that these vesicles are involved in hemagglutination, hemolysis, bacterial adhesion, and proteolytic activities.
• Anaerobic bacteria commonly produce short-chain fatty acids including propionic, butyric, and isobutyric acids. As virulence factors, these acids may affect neutrophil chemotaxis, degranulation, chemiluminescence, and phagocytosis.
• Polyamines are biologically active chemicals found in infected canals.