Virulence Factors Flashcards
What virulence factors contribute to adherence? Give examples
Adherence:
Adherence proteins: adherence proteins (adhesins) on pathogens bind to surface receptors on the host
Streptococcus pyogenes: M proteins bind to receptors on the respiratory mucosa
E. coli: colonization factor antigens (CFA) facilitate binding to small intestine
Fimbriae: Neisseria gonorrhoeae (fimbriae binding to urogenital tract)
Short filamentous structures, composed of protein, extend from the cell surface
Enable organisms to stick to surfaces
Form pellicles or biofilms
Pili:
Structurally similar to fimbriae
Typically longer
Usually, cells have only one or a few
What virulence factors contribute to invasiveness? Give examples
Invasiveness:
Capsules: interfere with the recognition of bacteria by phagocytes that engulf microbes
- Those with capsules seem more virulent
Other cell components:
Mycobacterium tuberculosis:
- Waxy cell wall with mycolic acid reduces phagocytosis
- If bacteria are engulfed, multiply inside phagocytes
Neisseria gonorrhoeae: when fimbriae and opa protein bind host cell, the host “takes up” bacteria
Enzymes: Virulence affected by exoenzymes
- Some bacteria produce leukocidins that kill white blood cells
- Some bacteria excrete hemolysin that lyses erythrocytes (RBC)
- Basis of hemolytic reaction
- Not clear how it impacts invasiveness
- Coagulase and kinases interfere with blood clotting (which repair wounds and prevent pathogens from invading)
Hydrolytic enzymes: - Hyaluronidase: hydrolyzes hyaluronic acid which holds connective tissues together
- Collagenase: hydrolyzes collagen which forms connective tissue
Antigenic variation:
- Host immune response makes antibodies that bind antigens (proteins)
- Antigen variation: pathogen alters cell surface antigens by activating alternative genes
- Immune response can’t keep up with how quickly the antigens are changing
Example: N. gonorrhoeae has many copies of the Opa gene to avoid immune response
