Ch 15: Microbial Mechanisms of Pathogenicity Flashcards
Define pathogenicity
- The ability to cause disease
- A property of an organism that it either has or lacks
Define virulence
- The extent of pathogenicity
- A measurement of the degree of pathogenicity that can be assessed
What are the most common portals of entry for diseases? (3)
- Mucous membranes
- Skin (hair follicles, sweat glands, surface)
- Parenteral route (penetration or injury)
What is the preferred portal of entry for SARS-CoV-2?
Mucous membranes of the upper respiratory tract
What is ID50?
Infectious dose of a toxin or pathogen for 50% of the test population
What is LD50?
Lethal dose of a toxin for 50% of the test population
What is the preferred portal of entry for Bacillus anthracis (anthrax)?
Skin
How do microbes adhere to a host cell?
Adhesins or ligands on the microbe bind to receptors on host cells
What are biofilms?
- Communities of adherent microbe
- Adhere to most surface with organic matter, a mix of polysaccharides and proteins
- Ex: dental plaque
What is the evolutionary benefit of capsulated bacteria?
- Increase virulence
- Prevent phagocytosis
What is the function of M protein in bacterial cell wall? Organism?
- Resist phagocytosis
- Streptococcus pyogenes
What is the function of Opa protein in bacterial cell wall? Organism?
- Inhibits helper T cells
- Neisseria gonorrhoeae
What is the function of Mycolic acid in bacterial cell wall? Organism?
- Waxy lipid
- Resists digestion
- Mycobacterium tuberculosis
What are exoenzymes?
Enzymes that work outside the bacterium to increase virulence
What is the function of the exoenzyme coagulase?
Coagulate fibrinogen
What is the function of the kinase exoenzymes?
Digest fibrin clots
What are invasins?
- Proteins that alter host actin to enter the host cell
- Causes membrane ruffling
- Ex: Salmonella
How do pathogens damage host cells? (4)
- Deplete host’s nutrients
- Cause direct damage
- Synthesize toxins
- Cause immune reactions
What does the DPT vaccine use as its delivery system?
- Toxoid (inactivated toxin)
What are exotoxins?
- Toxins secreted by a microbe that target a specific structure on or in the host cell
Do Gram+ or Gram- use exotoxins?
Gram+
Which type of toxin has a larger LD50?
Endotoxin
What type of biochemical are exotoxins?
Protein
Do exotoxins or endotoxins cause fever?
Endotoxins
What type of biochemical are endotoxins?
Lipid A from cell wall of Gram- bacteria
Are exotoxins or endotoxins neutralized by antitoxins?
Exotoxins
How do A-B Exotoxins function?
- A = active toxin; inhibits protein synthesis
- B = binds receptor on host cell; released
How do membrane-disrupting exotoxins function?
- Lyse host cell by:
- Making protein channels in plasma membrane
- Disrupting phospholipid bilayer
What are superantigens?
- Exotoxins carried by a prophage
- Caus an intense immune response due to release of cytokines from host cells
- Disables the host immune system
What are the major symptoms of superantigens? (6)
- Fever
- Nausea
- Vomiting
- Diarrhea
- Shock
- Death
Identify the toxin:
- Lysogenic phage caries tox gene that encodes an A-B toxin
- Causes severe skin lesion
- Part of the DPT vaccine
- Produced by Corynebacterium diphtheriae
Diptheria toxin
Identify the toxin:
- Superantigen
- Damages plasma membranes of capillaries in skin
- Causes Scarlet Fever, characterized by red skin rashes
- Produced by Streptococcus pyogenes
Erythrogenic toxin
Identify the toxin:
- A-B exotoxin
- Neurotoxin; inhibits acetylcholine at the neuromuscular junction
- Flaccid paralysis
- Produced by Clostridium botulinum
Botulinum toxin (aka Botox)
Identify the toxin:
- A-B exotoxin
- Neurotoxin; causes uncontrollable muscle contractions
- Produced by Clostridium tetani
Tetanus toxin
Identify the toxin:
- A-B exotoxin
- Enterotoxin; B-subunit binds to epithelial cells
- Causes cells to secrete fluids and electrolytes; severe diarrhea
- Produced by Vibrio cholerae
Cholera toxin
Identify the toxin:
- Superantigen
- Responsible for toxic-shock syndrome
- Interacts with MHC class II T-cell surface receptor
- Produced by Saphylococcus aureus
Staphylococcal enterotoxin
(Toxin = yellow, Receptor = green)
Why do endotoxins cause fevers?
- Cause macrophages to make cytokines (IL-1, aka TNF-alpha)
- Cytokines signal hypothalamus to release prostaglandins, which leads to fever
What is a LAL assay?
- Limulus amoebocyte lysate assay
- Detects very small amount of endotoxin
- Amoebocyte lysis produces clot
- Source: horseshoe crabs
Explain cytopathic viral pathogenesis
- Shut-down of host macromolecular synthesis
- Triggers apoptosis
- Inclusion body formation: aggregates inside cell
- Syncytium: fusion of cells
- Common among enveloped viruses
Explain transformation in regard to viral pathogenesis
- Inhibition of apoptosis
- Immortalization, loss of contact-inhibition
- Can lead to cancer
What is the receptor for SARS-CoV-2? Where is it abundant?
- ACE2
- Abundant in Type II alveolar cells and gut epithelium
What are the most common causes of death in regard to SARS-CoV-2 infection?
- Complications related to the kidneys
- Myocardial injury
