Bacterial Pathogenesis-General Flashcards
Describe the difference between extracellular and intracellular pathogens.
Extracellular pathogen: bacteria/parasite that replicates outside of host cells
Intracellular pathogen: bacteria/parasite that replicates inside host cells
What is an opportunistic pathogen?
Microorganism that will not cause disease in a healthy host, but will cause disease in individuals whose normal defense mechanisms have been compromised (burn patients, organ transplant recipients on immunosuppression, individuals with AIDS, pregnant women, patients with catheters).
What is an obligate intracellular pathogen?
A pathogen that cannot be found anywhere but in association with its host. Can grow only inside of host cells, cannot be cultured extracellularly. Ex. Chlamydia. All viruses are obligate intracellular pathogens.
What is a facultative intracellular pathogen?
Can grow/survive in environment as well as host. Can grow inside and outside of cells and be cultured on an agar surface in laboratory.
What is a virulence factor?
Component of the pathogen that contributes to its ability to cause an infection. Toxins, adhesions, proteins involved in immune evasion, iron acquisition, special adaptations of metabolism.
What are the three main ways in which bacteria breach the body’s barriers and cause disease?
- Intracellular growth of bacteria
- Disruption of host cell functions by extracellular pathogen
- Extracellular toxins that kill/alter host cells
What are different routes of entry/transmission?
Air-borne, water-borne, food-borne, vector-borne, via sexual contact, via a wound/cut. Many infections occur upon mucosal surfaces such as upper respiratory tract, lower intestinal tract, genitourinary tract. Some bacteria can cross placental barrier to pass from mother to child.
What are the benefits of intracellular bacterial growth?
Offers access to nutrients, allows bacteria to avoid extracellular defenses of host, and allows to cross barrier to reach deeper tissues.
What are some mechanisms by which bacteria evade extracellular host defenses?
- IgA protease- cleaves human IgA at hinge region, leaving only Fab fragments to bind antigens, Fc portion cannot signal phagocytosis
- Protein A- bind antibody to surface in the wrong orientation, bind Fc portion of IgG (S. aureus), doubles as a disguise of B-cells!
- Sialic acid- obtain sialic acid from host, and put on cell surface, minimally antigenic and thus an effective disguise
- Antigenic variation- important surface molecules display antigenic variation so that recurrent disease can occur with no effective immunity! (N. gonorrhoeae)
What is an A-B toxin?
Originally made as a single polypeptide chain, protein is cleaved into two protein chains, tethered by a disulfide bond. A portion contains catalytic function, B portion contains host cell binding and translocation functions. B portion binds to receptor on surface of susceptible host cells. Toxin internalized by receptor-mediated endocytosis. Drop in pH causes conformational change in toxin and triggers translocation of A portion into host cell cytosol. A portion free to find target in cytosol.
