Pathogenesis and Infection (Lec. 18) Flashcards
Identify the principal portals of entry for pathogens
Mucous membranes, skin, or parenteral route (deposited directly into tissues when barriers are penetrated,as in injections, bite wounds, cuts, or surgery). Most pathogens have a preferred portal of entry.
Define pathogen
Any microbe that can cause disease
Define true pathogen
Does not require a weakened host to cause disease (never part of normal microbiota)
Define opportunistic pathogen
Agents of disease under certain circumstances (only cause disease when the host is weakened, can be normal microbiota that enter a different body site). Ex: often fungal infections.
Define pathogenicity
The quality or character that a pathogen has, which is the ability to cause disease
Define virulence
Often used interchangeably with pathogenicity, but usually a comparative or relative term (the degree or extent of disease that a pathogen causes)
Define virulence factor
Microbial products or characteristics that increase ability to cause disease (adhesion, invasion, toxins, immune system evasion, nutrient acquisition)
Define LD50
The number, calculated in a laboratory setting, of how many cells or particles would be required to kill 50% of your test subjects
Define ID50
The number calculated in a laboratory setting of how many cells or particles would be required to get 50% of your test subjects infected.
Define attenuation
Loss of virulence factors, in that the pathogen is still infectious but it’s weakened.
Explain how capsule and cell wall components contribute to pathogenicity
Many adhesins (surface proteins, fimbriae, pili, flagella, biofilms, etc.) aid in pathogenicity. A capsule can impair phagocytosis.
Compare the effects of coagulases, kinases, hyaluronidase, and collagenase
Coagulases coagulate fibrinogen, forming fibrin, which creates a barrier for itself. Kinases can digest fibrin clots, which can be virulence factors for bacteria that want to penetrate deeper into tissues. Hyaluronidase digests hyaluronic acid, which is a host polysaccharide that holds cells together. Collagenase breaks down collagen
Define and give an example of antigenic variation
Antigenic variation occurs when pathogens alter their surface antigens (and therefore the antibodies that a host made against those antigens are now rendered ineffective). Ex: influenza, Neisseria gonorrhoeae, Trypanosome brucei gambiense
Describe invasins and how bacteria use the host cell cytoskeleton to enter the cell
Surface proteins that help an organism invade a host cell (can rearrange actin filaments and cause membrane ruffling and/or endocytosis).
Compare/contrast endotoxins and exotoxins
Exotoxins are bacterial proteins (secreted by living bacteria) that target specific cells but can be neutralized by an antibody. Endotoxins are lipopolysaccharides that are part of a Gram negative cell membrane. When the cell dies, Lipid A is released and triggers an excessive inflammatory response, which puts the host organism into shock.
Define toxin vs. antitoxin
Toxins are molecules that generate adverse host effects. Antitoxins are antibodies that counteract a toxin.
Define toxoid
A chemically modified toxin that is no longer toxic but is still antigenic and can be used as a vaccine.
Define toxigenic
Toxigenic microbes are microbes that make toxins.
Define intoxication
A presence of toxin without microbial growth.
Outline the mechanisms of action of exotoxin types
Type 1: extracellular, binds to a host cell and exerts its toxicity from there (superantigens). Type 2: extracellular, target cell membranes and cause lysis (leukocidins, hemolysins, streptolysins). Type 3: intracellular, bind to a receptor and enter the cell (most in this group are A-B toxins, B meaning binding region and A meaning active portion that exerts effects inside).
Define cytopathic effects and give five examples
Cytopathic effects are visible effects of viral infections. Disrupting cell junctions, inducing a cytokine storm, stopping macromolecular synthesis within cells, causing host cell lysosomes to release enzymes (causing cell death), creating inclusion bodies in the cell cytoplasm, fusing host cells to create a syncytium, antigenic changes on host cell surface, viral-induced chromosomal damage, transformation of host cells (loss of contact inhibition)
Discuss pathogenic properties of fungi
Produce a lot of toxic metabolic products, can provoke an allergic response, can release toxins that inhibit protein synthesis, can produce proteases that damage cell membranes, some yeasts have capsules that prevent phagocytosis.
Discuss pathogenic properties of protozoa
Presence of protozoa and their waste products cause symptoms of protozoan diseases. They avoid host defenses by digesting cells and tissue fluids and having antigenic variation. They grow in phagocytes.
Discuss pathogenic properties of helminths
They use host tissue for growth and produce large parasitic masses that cause cellular damage that can cause obstructions in the lungs and bowels.
