Virulence and Pathogenicity - Bacteria Flashcards
Why is a capsule so important to the bacteria?
• Major virulence factor to evade clearance
• Protection form host immune response and
antibiotics
• Protection from phagocytosis and opsonization
What is the cell wall of the bacteria for?
- Both gram positive and gram negative
- Toxic components in their cell wall
- Can cause shock whether intact or after antibiotic treatment and bacterial cell death
What is lipopolysaccharide (LPS)?
WILL BE ON EXAM
- Gram negative bacteria only
- Large amphophilic molecule found in outer bacterial membrane
- Receptor on macrophages
- Lipid A portion triggers release of cytokines and initiates complement cascade
- Outside of the cell to trigger the immune response.
What are the toxins of a bacteria?
- Proteinaceous or non-proteinaceous molecules
- Produced to damage or destroy host cells
- Proteinaceous are exotoxins from Gram negative bacteria
- Non-proteinaceous are toxins such as LPS
What are the delivery systems of the exotoxin?
Secretion into the surrounding environment, or direct injection into the cell
What are the ways exotoxin breaks down a host cell?
- Enzymatic activity, binding and delivery of toxin
- Proteolytic break down of host proteins
- Membrane disrupting toxins – pore formation
- Toxins against IgA and host cytoskeleton
What are adhesins?
- Expression of factors to allow bacteria to bind to host cells
- Avoid removal or washing away of bacteria via host mechanisms
- Once adhered can proceed with proliferation, toxin delivery, cell invasion, and immune responses of host
What are the types of adhesins?
- Polypeptides (proteins) or polysaccharides
- Protein adhesins can be fimbrial or afimbrial
- Gram negative use fimbriae ***
- Afimbrial adhesins have more intimate contact usually along the cell wall of the bacteria
What are extracellular invasins?
- Extracellular or intracellular
- Extracellular uses enzymes which break down cell integrity of host allowing invasion of tissue
- Enzymes such as hemolysins, hyaluronidase, and nucleases
What are intracellular invasins?
- Intracellular invasion occurs when whole organism enters the host cell
- Obligate or facultative intracellular
- Internalization or phagocytosis of the bacteria
- Can proliferate and spread cell to cell
How do bacteria survive inside a cell?
- Non-phagocytic cells and professional phagocytes. Avoidance of proteases and reactive oxygen intermediates
- Examples are Chlamydia, Rickettsia, and Listeria
- Acidic phagolysosome (Phagosome with no fusion to a lysosome, within host cell cytosol) Can lyse vacuole and then use host cytoskeleton to escape the cell
Name the regulation of virulence factors
- Survival depends on ability to sense and respond to environmental cues
- Rapid adaptation by bacteria is necessary to allow colonization and growth
What are sigma factors?
- Protein subunits of RNA polymerases which control transcription
- Bacteria use different sigma factors to control gene expression of virulence factors
- Can control mucoid phenotypes and flagellar expression in pathogens
What is the two component system?
- Sensor proteins and response regulators
- Sensors in bacterial membranes to sense physiologic conditions in the cell
- Response regulator which can activate or repress transcription
- Involved in regulation of iron and other molecules
How do bacteria become pathogenic?
- Generally, it is through the acquisition of “bad genes”
- Horizontal gene transfer – molecular evolution of novel pathogens
- Donor to recipient – blocks of DNA which contain large mobile genetic components
- Pathogenicity islands – contain virulence factors such as adhesins, invasins, toxins
- Not present in non-pathogenic strains
