18-Mechanisms of Bacterial Pathogenesis Flashcards
What is the mechanism of action of the superantigen?
Superantigen: These molecules activate T cells by binding simultaneously to a T-cell receptor and a major histocompatibility complex class II (MHC II) molecule on an antigen-presenting cell without requiring antigen. Activate large numbers of T cells to release large amounts of interleukins (cytokine storm), including IL-1, TNF, and IL-2, causing life-threatening autoimmune-like responses.
What bacteria produce the superantigen?
S. Aureus: Toxic Shock Syndrome Toxin
Staph enterotoxins
S. pyogenes: Erythrogenic toxin A or C
What is the difference between an endotoxin and an exotoxin?
Exotoxins are made by both gram- and gram+ and are released by the bacteria
Endotoxins are made only by gram- bacteria and are maintained w/in the bacteria, however lyse/killing endotoxin containing bacteria at once will release the toxin into circulation and can cause death.
What is the clinical presentations of a low concentration of endotoxin?
At low concentration endotoxin stimulates protective responses of the body such as fever, vasodilation, and activation of the immune system
What are the clinical presentations of high concentration of endotoxin?
At high concentration of endotoxin (such as gram- bacterial sepsis) the systemic response can be overpowering and result in shock and death
What is the mechanism of action of the diptheria toxin?
Fragment B of the toxin binds to the cell which signals the cell to internalize the toxin via receptor mediate endocytosis w/in an endosome. The acidity of the endosome causes fragment B to create pores in the endosome membrane, thereby catalyzing the release of fragment A into the cell’s cytoplasm.
Fragment A inhibits protein synthesis by inactivating elongation factor 2 which leads to cell death.
Why is the capsule so super crazy?
The capsule is one of the most important virulence factors, because it shields the bacteria from host defenses such as immune and phagocytic responses. They are usually polysaccharides which are poor immunogens.
The capsule also allows the bacteria to get away from a phagocyte if it is grabbed. The capsule also protects the bacteria from degradation w/in phagolysosome of macrophage.
What is antigenic drift?
Antigenic Drift: A mechanism for variation by viruses that involves the accumulation of mutations within the antibody-binding sites so that the resulting viruses cannot be inhibited well by antibodies against previous strains making it easier for them to spread throughout a partially immune population. Antigenic drift occurs every 2 to 3 years in both influenza A and influenza B viruses leading to local outbreaks
What is antigenic shift?
results from reassortment of genomes among different strains of a virus, including animal strains. The consequence of this reassortment is usually a pandemic, or a worldwide epidemic. Only occurs in with the influenza A virus.
What is antigenic variation?
a mechanism by which organisms can escape the immune surveillance of a host by modifying or completely altering their surface antigens
