5.9 - Bacterial Virulence Strategies Flashcards
Define Virulence
Factors that cause disease in host cells
What are four things a pathogen must do to cause disease?
1) Gain access to host
2) Adhere to host tissues
3) Evade host defenses
4) Damage host tissues
What is our first line of defense against pathogens?
Skin, mucous membranes, and normal microbiota
What is our second line of defense against pathogens?
Phagocytes, inflammation, fever, antimicrobial substances
What is our third line of defense against pathogens?
T and B cells, and antibodies
What are the 3 factors that determine the outcome of infection?
1) Integrity of host defenses
2) Number of microorganisms
3) Virulence of microorganism
Where are the virulence genes located?
1) Chromosome
a) Pathogenicity islands are unique region exclusively associated with virulence, complete package required for delivery of pathogenic trait
2) Plasmids or bacteriophages
How do pathogens get around host innate defenses?
1) Phagocytes
A) Gram positive lipotechioc acid
B) Gram negative LPS
2) Host iron binding molecules
What is a siderophore?
Bacterial virulence factor such as host iron binding molecules.
What are types of adherence?
1) Bacterial adhesion to host receptors
2) Examples: Pili, OM proteins/sugars, CW proteins, teichoic acids.
What are some examples of hydrolytic enzymes released by microbes?
Proteases, hemolysins, neuraminidase, collagenase, hyaluronidase, elastase, DNAase, coagulase.
What are main characteristics of Exotoxins?
- Secreted
- Protein
- Heat sensitive
- Classified as neurotoxins/enterotoxins.
- Often encoded by plasmids, bacteriophages
- Can be Gram positive or negative
- Can be neutralized by antitoxin
- Takes a small amount to kill host.
What are main characteristics of Endotoxins?
- In OM also released by dying/dead cells.
- Lipid A
- Heat Stable
- Only Gram negative
- Causes fever
- Cannot be neutralized by antitoxin
- Takes a large amount to kill host.
What is a superantigen?
- Binds MHC molecules on antigen presenting cells without processing, and directly stimulates cytokine production.
- Non-specific activation of T-cells resulting in polyclonal T cell activation and massive cytokine release
- Can activate up to 20% of bodies T-cell, normal antigen actives about .0001% of T-cell
- Viruses, bacteria, and fungi can form this
What is an A-B exotoxin?
B- binds to specific host receptors
A- enters cell and enzymatically attacks host function or structure.
(example Vibrio cholerae A-B enterotoxin)
