Bacterial Virulence Factors

• Virulence factors are mechanisms that determine the degree to which pathogens cause damage, invasion, and infectivity, and help microorganisms invade and avoid host defenses.

Key Terminology

• A pathogen is any microorganism that can cause disease in a host organism.
• A primary pathogen is an environmental microbe that can cause disease in an otherwise healthy individual.
• An opportunistic pathogen is a member of the normal microbiota that only causes disease in an immunocompromised host.
• Pathogenicity is the ability of a pathogen to cause disease.
• Virulence is the degree or intensity of pathogenicity.
• Antigenic drift results from point mutations causing minor changes in spike proteins.
• Antigenic shift results from gene re-assortment causing major changes in spike proteins.
• Cytokines are small proteins that control immune cell growth and activity.

Virulence Factor Mechanisms

• Proteases degrade collagen in connective tissue to promote spread.
• Exoenzymes are secreted by the cell and function outside of it.
• Invasion starts the invasion process and allows penetration of deeper tissues, and is specific to particular tissue structures.
• Pili are hair-like structures that enable bacteria to attach to host cells, colonize and allow the bacteria to move along the host cell surface.
• Fimbriae alter the surface of bacterium to prevent phagocytosis; some streptococcus species contain M protein that alters the surface wall of bacteria to inhibit phagocytosis.
• Adhesion is the mechanism by which bacteria adhere closely allowing for colonization
• The bacterial cell wall contains surface proteins that bind to target receptor molecules on host cell surfaces, allowing bacteria to adhere closely.
• Capsules are protective coats that prevent phagocytosis from immune cells, prevent adhesion of antibodies and aid in adhesion of bacteria.
• Mycolic acid is produced in the cell wall and acts as a protective coat, deterring killing mechanisms when phagocytosed.
• Immune evasion is the process by which the bacteria avoid detection and destruction due to altering surface proteins.
• Leukocidins are cytotoxins that can destroy white blood cells and phagocytes (immune cells).
• Toxins are biological poisons that are produced by some pathogens.
• Exotoxins are potent protein molecules produced inside pathogenic bacteria, mainly by gram-negative bacteria; they target specific receptors on specific cells and are lethal in low concentrations.
• Endotoxins are derived from gram-negative bacteria, stimulate a general systemic inflammatory response, are stable at high temperatures and are part of the outer membrane of the bacterial cell wall; low concentrations trigger a host inflammatory response, and high concentrations cause a severe drop in blood pressure, multi-organ failure, or death.
• Toxigenicity is the ability of a pathogen to produce toxins and cause damage to host cells.
• Adhesins are different for different functions of adhesion to oral epithelial cells and biofilm formations.
• Pleomorphism allows organisms to respond to various environmental conditions and adapt to biological niches.
• Candida albicans is a pathogenic yeast that causes oral thrush.
• Exoenzymes are produced in a variety of forms that contributes to tissue damage and adhesion, and releases iron for nutrition.
• Gingipains are exoenzymes (proteases) are produced by gingipains to break down structural proteins of periodontium (collagen, elastin & fibronectin) and contribute to periodontal disease.
• Fimbriae modify and stimulate immune responses in periodontium and effects cytokine secretion and inhibition.

Virulence Factor Mechanisms in Oral Health

• Porphyromonas gingivalis is a gram-negative anaerobe that causes periodontal disease
• Adhesin (Adhesin P1) anchors to the cell wall and aids with adhesion to the tooth
• The polysaccharides on cell wall aid bacteria to adhere to tooth enamel.
• Surface glycoproteins coat with complement factors to prevent the immune system from eliminating it.
• Herpes simplex virus (HSV-1) is a pathogenic virus.
• Cell surface receptors are used both gain entry and spread from cell to cell.
• Opportunistic pathogens hide in neurons and non-neuronal cells, emerging as a pathogenic form when immune resistance is low.
• Streptococcus mutans is a gram-positive facultative anaerobe that causes caries.
• Acidogenic bacteria produce acid by breaking down carbohydrates. The causes a decrease in the oral cavity pH which increasing cariogenic bacteria increases the risk of tooth decay.
• Cariogenicity is the ability to promote or cause the development of tooth decay.