Intro to Infectious Diseases, Cell Structure and Classification, Virulence Flashcards
Virulence:
The ability of an organism to cause disease.
Three routes of disease transmission:
- Exogenous microbes transmitted from one human to another human.
- Exogenous microbes transmitted from animals to human.
- Endogenous agents which are part of the normal flora.
Fomites:
Inanimate objects which harbor microorganisms.
Beneficial effects of normal flora (4):
- Production of essential nutrients (vit. K).
- Occupation of habitat.
- Elaboration of toxic products.
- Stimulation of the host immune response.
Koch’s Postulates(4):
- Bacterium should be found in all people who have the disease in parts of the body affected.
- Bacterium should be isolated and maintained in pure culture.
- Pure culture inoculated into another should produce disease symptoms.
- Same bacterium should be reisolated in pure culture.
Limitations/caveats to Koch’s postulates(5):
- Ignores the role of host.
- Importance of being able to culture bacterium.
- Variability in virulence of a single bacterial species.
- Ethical problems with 4th postulate.
- Polymicrobial infections.
Two types of viral infections:
- Lytic cycle
2. Persistent or latent infections.
Viroids:
Consist of RNA genome without any protein components.
Prions:
Infectious agents consisting only of protein.
Pili:
Thin, rigid appendages composed of proteins called pilins.
Allow cells to adhere to host cell or other bacterial cell surfaces.
Cytoplasmic inclusion bodies:
Sites where nutrient macromolecules are stored as large complexes.
Bacterial plasma membrane functions (3):
- Site of active transport.
- Respiratory chain components.
- Site of synthesis for phospholipids, peptidoglycan, LPS and capsular polysaccharides.
Bacterial cell envelope =
Plasma membrane + cell wall + intervening material
Gram positive cell envelope key features (3):
- Thick, multilayered peptidoglycan overlying plasma membrane.
- Teichoic acids, lipoteichoic acid.
- Plasma membrane
Peptidoglycan functions/activities (4):
- Allows diffusion of small molecules to the plasma membrane.
- Confers rigidity and shape.
- Interferes with phagocytosis.
- Adjuvant, pyrogen and somnagen
Teichoic acids:
Water-soluble polymers of either ribitol phosphate or glycerol phosphate that are covalently linked to peptidoglycan.
Lipoteichoic acids:
Teichoic acids which terminate in a fatty acid that serves to anchor the molecule in the plasma membrane.
Gram negative envelope key features (4):
- Unique outer membrane which contains LPS.
- Thin peptidoglycan overlaying plasma membrane.
- Periplasmic space.
- Inner (plasma) membrane.
Which portion of LPS is responsible for endotoxic activity?
Lipid A
Results of LPS in the bloodstream:
Synthesis of IL-1, TNF and other cytokines; complement and coagulation cascades are activated.
Braun lipoprotein:
Covalently anchors the outer membrane to peptidoglycan. (Inner leaflet of outer membrane.)
Omp proteins:
Stabilize the outer membrane and act as specific receptors.
Three types of exotoxins:
- AB toxins.
- Pore-formers (hemolysins).
- Superantigens
Pore former exotoxin:
Acts to lyse the cell by permitting rapid water entry in response to the osmotic gradient.
Phospholipase:
Enzymatically removes the charged head of phospholipids. Destabilizes the cell membrane, resulting in cell lysis.
Adhesins
Bacterial surface proteins which mediate intimate contact with the host cell.
Bacteria obtain iron (3):
- Siderophores/enterobactins chelate iron and bring inside cell.
- Receptors for transferrin, lactoferrin, etc.
- Kill host cells to liberate intracellular iron.
