9. Infection II Flashcards
(22 cards)
What is the first step in the infection process?
Pathogen must encounter and attach to host
List the key steps in the infection process.
- Facilitate entry and establish presence
- Colonize host tissues
- Develop mechanisms for multiplication and spread
- Eventually shed to infect new hosts
True or False: Infections are always symptomatic.
False
What are some general pathogenic strategies?
- Produce capsules to frustrate phagocytosis
- Generate lipopolysaccharides (LPS) that can cause septic shock
- Secrete toxins that aid invasion and cause host cell damage
- Express adhesins (including lectins) to facilitate attachment
- Produce enzymes (proteases, glycanases) to break down host matrix
- Develop mechanisms to survive within phagosomes or cytosol
What are host defenses against pathogen attachment?
- Rinsing microbes away from epithelial surfaces
- Secretions (e.g., mucin in respiratory tract)
- Ciliary activity to clear pathogens
- Production of immunoglobulin A (IgA)
Name a pathogen countermeasure against host defenses.
- Surface molecules that bind to specific host receptors
- Production of toxins that inhibit ciliary activity
- IgA proteases that break down host antibodies
- Formation of microcolonies (as seen with enteropathogenic E. coli)
- Fimbriae/pili that bind to mannose receptors (e.g., E. coli type 1 fimbriae)
What physical barrier does the host present against invasion?
Cell membrane
What are some pathogen mechanisms for invasion?
- Fusion proteins (e.g., HIV envelope proteins)
- Injection of proteins that trigger uptake
- Blocking intracellular killing mechanisms
Give an example of a pathogen that uses fusion proteins for invasion.
HIV
How does Listeria monocytogenes facilitate cell-to-cell spread?
Uses ActA protein to polymerize actin, forming ‘rocket tails’
What is the role of siderophores in iron acquisition?
Pathogens secrete siderophores (iron-binding molecules) with higher affinity for iron than host transferrin/lactoferrin
How do pathogens resist oxidative burst from host phagocytes?
- Diverting vesicles containing NADPH oxidase
- Producing enzymes (catalase, superoxide dismutase) to detoxify reactive species
- Breaking down hydrogen peroxide before hydroxyl radicals form
What strategies do pathogens use to evade complement and antimicrobial peptides?
- Sialylation of bacterial surface (stealth mode)
- Alterations to lipopolysaccharide structure
- Production of proteases to degrade antimicrobial peptides
- Expression of C3b receptors to interfere with complement cascade
How do pathogens evade antibodies?
- Secretion of IgA proteases
- Infecting lymphoid cells to hide within immune system
- Binding antibodies in unusual orientation
- Extended LPS chains to keep antibodies at a distance
- Acquiring coating of host molecules (fibrin, actin)
What is one method pathogens use to shed and increase transmission?
- Trigger sneezing/coughing via respiratory route
- Cause diarrhea via fecal-oral route
Describe the composition of Vibrio cholerae cholera toxin.
- Composed of A1, A2 catalytic units surrounded by five B units
- B units bind to GM1 ganglioside receptors
What is the LD50 of botulinum toxin type D?
0.8×10⁻⁸ mg
What are the characteristics of Enterohemorrhagic E. coli (EHEC)?
- Major foodborne pathogen
- Causes diarrhea, hemorrhagic colitis, hemolytic uremic syndrome (HUS)
- Typically O157 serotype
What are the pathogenicity mechanisms of EHEC?
- Shiga-like toxins (Stx1 and Stx2)
- Locus of Enterocyte Effacement (LEE)
- Multiple infection routes
What is the function of Shiga-like toxins in EHEC?
Inhibit protein synthesis
What does the Locus of Enterocyte Effacement (LEE) encode?
Type III secretion system (‘molecular syringe’)
What is the outcome of the dynamic conflict between host defenses and pathogen virulence factors?
Depends on microbial virulence, infectious dose, and host immune status
