Final > Molecular Basis of Infection Flashcards
Define pathogenicity.
The ability to cause disease.
Define virulence.
The degree of pathogenicity (ability to cause disease).
What are the 3 main portals of entry for microorganisms to enter a host?
- Mucous membranes
- Skin
- Parenteral route (cut)
What is meant by ID₅₀?
A measure of the infectious dose necessary to infect 50% of the population. (virulence)
What is meant by LD₅₀?
A measure of the lethal dose necessary to kill 50% of the population. (potency)
What can have an effect on the ID₅₀ of a microorganism?
Environmental/chemical factors. Ex: lime increases the infectivity of Cryptosporidium parvum.
By what process do pathogens attach to host tissues?
By adherence (adhesion), where adhesins (ligands) on the pathogen bind to receptors on the host cell.
What is a glycocalyx?
A carbohydrate coating on the outside of many bacteria.
What is the function of M protein on the surface of a microorganism?
To resist phagocytosis by the host immune system.
What is the function of OPA protein on the surface of a microorganism?
To allow attachment to the host cells.
What is the function of waxy lipid (mycolic acid) on the surface of a microorganism?
To resist digestion.
How can antigenic variation help microorganisms survive in the host?
The microorganism alters its surface antigens, rendering antibodies ineffective.
What is the purpose of an invasin? In what 2 ways can it help a microorganism
A bacterial surface protein
- Rearranges actin cytoskeleton to allow entry into host
- Rearranges actin to allow transmission to new hosts
What is a siderophore?
A protein secreted by a pathogen which can bind iron more tightly than the host cell can, making it available for the pathogen.
What part of the antigen does IgA target? What is characteristic of this region?
Targets the middle region of the antigen which is rich in proline.
What is an example of a bacterial siderophore?
Enterobactin.
In what 4 main ways can pathogens cause direct damage to a host cell?
- Disrupt host cell function
- Use up host cell nutrients
- Produce waste products
- Multiply and lyse host cell
Define toxigenicity.
The ability of a microorganism to produce a toxin.
What is an exotoxin?
A protein produced and secreted by bacteria that is soluble in body fluids and has harmful effects.
What are 2 examples of inactivated exotoxins that are used in vaccines?
- Diptheriae vaccine
2. Tetanus vaccine
Describe the 2 components of A-B toxins.
- A = enzyme component
2. B = binding component
What are some examples of A-B toxins?
Diptheria toxin, Pertussis toxin, Tetanus toxin, Botulin, Cholera toxin, etc.
What 4 steps outline A-B toxin function?
- Bacteria releases toxin
- B component binds to host cell
- Endocytosis of toxin
- A component released into cytoplasm, alters function
What is the function of a membrane-disrupting toxin?
To disrupt the host plasma membrane, resulting in lysis.
What is a leukocidin?
An exotoxin which kills phagocytic leukocytes.
What is a hemolysin?
An exotoxin which kills erythrocytes by forming protein channels.
What is a streptolysin?
A hemolysin produced by streptococci.
What is a superantigen?
An exotoxin which releases cytokines from host cells, causing an intense immune response.
What is a genotoxin?
An exotoxin which damages DNA by causing mutations, potentially disrupting cell division and leading to cancer.
What is the main structural difference between exotoxins and endotoxins?
Exo: protein-based
Endo: lipid-based
What type of bacteria most commonly release endotoxins? When do they do this?
Gram negative bacteria release them during replication and cell death (from membrane).
How do endotoxins act on host cells? What deadly symptom can result?
Stimulate macrophages to release cytokines. Can cause disseminated intravascular coagulation.
What assay is used to test for endotoxins? How does it work?
Limulus amebocyte lysate (LAL) assay. In the presence of endotoxins the amebocytes lyse and produce a clot.
What type of bacteria most commonly release exotoxins?
Gram positive bacteria.
In general, how do the effects of exotoxins differ from those of endotoxins?
Exo: specific effect
Endo: generalized effect
Which type of toxin (endo or exo) is most stable in heat?
Endotoxins. They can even withstand autoclaving! Crazy!
What does “lysogenic conversion” mean?
A change in the characteristics of a microbe due to the incorporation of a prophage.
What is meant by “cytopathic effects” (CPE)?
The visible effects of viral infection on a cell.
What are some examples of cytopathic effects?
- Cell synthesis stops
- Lysosomes release enzymes
- Fusing multiple cells
- Changing host function
- Chromosomal changes
- Inducing surface antigens
- Loss of contact inhibition
- Production of interferons
What is a syncytium?
A single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei.
What is an inclusion body in terms of cell anatomy? What are they indicative of?
Protein aggregates in the cytosol or nucleus. Indicate sites of viral replication.
Who was the first to show that Rous sarcoma ( a type of fibroblast cancer) was caused by a retrovirus? When?
Howard Temin in 1960 (retrovirus = RNA virus with a DNA stage)
What are the 5 main portals of exit for microorganisms to leave a host?
- Respiratory tract (ex: cough)
- Gastrointestinal tract (ex: spit or shit)
- Genitourinary tract (ex: pee + other fluids)
- Skin (sweat?)
- Blood (ex: bug bites)
