Micro22 Microbial Mechanisms of Pathogenicity

Portal of entry: skin, mucous membrane, or most frequently the mouth

Portals of exit: same portal for entry and exit, most common are respiratory tract, GI tract, or genitals

Infective dosage (ID) of Pathogen: likelihood of disease increases as number of pathogens increases, the actual number of pathogens required to infect (can’t be use to tell the severity of the pathogen)

• ID 50: infective dosage for 50% of individuals

• LD 50: lethal dosage for 50% of individuals

Bacteria adhere to host tissues through: Bacteria surface molecules called adhesins, biofilms through capsule, fimbriae, and hook

How pathogens penetrate host defense?

• Capsule: resists host phagocytosis

• Cell wall components: M protein and mycolic acid (wax coating) to resist phagocytosis

• Enzymes: coagulase, kinase, hyaluronidase, collagenase

How pathogens destroy host cell?

• Direct damage: use host cell for nutrients for metabolism and multiplication

• Production of toxins:

  • Exotoxins: produced inside then secrete to outside, ie. leukocidins, streptolysins, hemolysins, AB toxins

    • Released from living bacteria

    • Come from both gram-positive and gram-negative

    • Protein

    • More toxic

    • Specific effects

    • Sensitive to heat (heat labile)

    • Often antigenic (can produce vaccines against them)

  • Endotoxins: part of outer portion of cell wall of gram-negative bacteria

    • Released following death of bacteria

    • Come from gram-negative only

    • Lipopolisaccharides

    • Less toxic

    • More general effects

    • Heat stable

    • Not antigenic, no vaccine