LG5.9 bact virulence strat Flashcards
Define virulence.
•extent of pathogenicity –E.g. number of virulence factors
Where are bacterial virulence genes located?
- chromosome (pathogenicity islands - these can also be on plasmids). they are unique region exclusively associated w/ virulence - complete island required for delivery of pathogenic trait
- plasmids
- inside bacteriophages
Discuss how bacterial cells adhere to host cells.
–bacterial adhesin↔host receptor
bacteria use ‘adhesin’–E.g. •pili, OM proteins/sugars, CW proteins, teichoic acids
what are hydrolytic enzymes? what’s their role as a virulence factor?
- chew up material - help with digestion and digging into tissues (invasiveness) (eg, proteases, hemolysins, neuroaminidase, collagenase, DNase, etc.
- Cause host tissue Injury
Give some characteristics of exotoxins
- these are virulence strategy (tissue injury)
- secreted
- Gr+ or Gr-
- protein
- causes fever somtimes
- neutralized by antitoxin
LD50 is small
-most heat-sensitve
Give some characteristics of Endotoxins
these are virulence strategy (tissue injury)
- on OM
- Gr- only
- Lipid A constituent
- always causes fever
- not neutralized by antitoxin
LD50 is large
-most heat-stable
List some types of extoxins
- A-B exotoxins (B ‘B’inds to specific host receptors) (A (‘A’ctive) enters cell and enzymatically attacks host function or structure (eg Vibrio cholerae A-B enterotoxin)
- pore-forming exotoxins
- superantigens
- type III secretion system
What are superantigens?
-Exotoxin (virulence factor that causes tissue injury)
•non-specific activation of T-cells resulting in polyclonal T cell activation and massive cytokine release
(bind MHC molecules on antigen presenting cells (w/o processing) and directly stimulate cytokine production→ massive activation of T cells→ uncontrolled release of cytokines→ inflammation→ shock)
What are type III secretion systems?
-exotoxin (virulence factor that causes tissue injury)
»only in Gr-
»‘syringe’ for injecting toxic molecules into host cells (traverse envelope)
-never exposed to immune system
»no virulence w/o
Why is do some bacteria thrive INSIDE of host cells?
- easier to evade host defenses INSIDE of our cells vs outside
- facultative intracellular
- obligate intracellular
how do capsules protect some bacteria?
-virulent strategy (evading host defense)
- interferes w/ complement deposition
- interferes w/ phagocyte engulfment
- eg, Streptococcus pneumoniae
List six ways bacteria evade the host immune system
- invade cells
- capsules
–phase variation eg, Neisseria gonorrhoeae
–antigenic variation eg, Neisseria gonorrhoeae
–IgA1 protease eg, mucosal pathogens, Neisseria gonorrhoeae
–biofilms - common strategy!
How is antibiotic resistance used as a virulence strategy?
–innate (eg mycoplasma has no cell wall - so Antibx that target cell wall won’t work)
–acquired (mutation, gene exchange)
–biofilms
what is phase variation?
- way to ‘evade host defese’
- bacteria’s ability to turn on and off its surface molecules so the bacteria will look different during infection
eg, Neisseria gonorrhoeae
what is antigenic variation?
- way to evade host defense
- bacteria’s ability to change surface antigens
eg, Neisseria gonorrhoeae
what is IgA1 protease?
this clips the antiody at the hinge
eg, mucosal pathogens, Neisseria gonorrhoeae
What are 2 virulence factors that help bacteria gain entry to the cell?
–phagocytes (capsules)
–host iron-binding molecules (bacterial virulence factor known as ‘siderophore’)
