Bacteriology 4: Bacterial Pathogenesis (diagnosis Is Separated) Flashcards
Define virulence factor:
Bacterial constituents that promote infection
Steps in pathogenesis
Encounter: endogenous or exogenous
Entry: access- (toxins).. penetration of epithelial barrier
Spread: adjacent tissues to distant tissues
Multiply: incubation period/ immune evasion
Damage: disease (clinical/subclinical). Immunopathology (how the immune system response contributes to the development of the disease)
Outcome: symbiosis w/ organism. Clearance of organism. Death
What type of pathogens cause disease even in healthy hosts?
True/primary pathogens
Opportunistic pathogens
Cause disease under immunocompromised or unusual conditions
What is dependent on the severity of the disease?
The condition of an individual plays an important role in whether disease occurs (age, health, ability of the host to protect itself)
Virulence of the organism and susceptibility of the host is what the disease severity is dependent on
What do Virulence and virulence factors do?
What are some examples of virulence and virulence factors?
Virulence factors help the microbe adapt and/or invade the host. Virulence factors are critical for the pathogen’s ability to survive and proliferate in the host, and they may be encoded on various genetic elements, such as the chromosome, plasmids, or phage genomes (viruses that infect bacteria).
-adhesion (Fimbriae, pillie, binding factors)
-invasion (flagella, various toxins, enzymes) Pathogens produce enzymes that break down host tissues and allow them to invade deeper into the body.
Example: Streptococcus pyogenes produces hyaluronidase, which breaks down hyaluronic acid in connective tissues, facilitating spread
-toxins (LPS) Toxins disrupt host cell functions or directly cause cell death, leading to tissue damage and disease symptoms.
Example: Clostridium botulinum produces botulinum toxin, which blocks nerve function, causing paralysis
-immune system evasion(capsule, enzymes, toxins) Streptococcus pneumoniae has a polysaccharide capsule that prevents phagocytosis by immune cells.
-nutrient acquisition (diverse enzymes, iron-binding proteins) Some pathogens produce enzymes that break down host molecules to acquire nutrients.
Example: Staphylococcus aureus produces hemolysins that lyse red blood cells to obtain iron.
Virulence= the degree or strength of pathogenicity
Virulence factor= bacterial molecules that promote infection
Infectious dose (ID50) vs. Lethal Dose (LD50)
-what type of relationship do they have?
-an example of a bacteria that is more virulent vs. one that is less virulent?
These are metrics used to assess the virulence or potency of a pathogen
-ID50= number of organisms required to cause infection in 50% of infected organisms
-LD50= number of organisms required to kill 50% of infected organisms
ID50 & LD50 have an inverse relationship with virulence. Therefore a low ID50/LD50 will have a high virulence
More virulent bacteria
= Francisella Tularensis(Rabbit fever)
=has a very low infectious dose (ID50) therefore is highly virulent
Less virulent bacteria
= Lactobacilli, diphtheroids, cholera Vibrio cholera
=has a very high infectious dose (ID50) therefore is less virulent.
Adherence factors
-involves?
-what are some receptors and adhesion factors?
-example of a bacteria?
attachment mechanism
-adherence involves host receptors and bacterial adhesions
-host receptors = glycoproteins and sugars
-adhesion = Fimbriae, pillie, Flagella, Biofilm, binding factors
Flagella = composed of flagellin (motility)
(H antigen)
Fimbriae = shorter than Flagella
Pili = tubular structure
Biofilm = community of microorganisms embedded in a self-produced ECM attached to a surface
-Vibrio cholerae attaching to the intestinal epithelia
-E.coli attaching to intestinal microvilli
-Neisseria gonorrhoeae uses pili to attach to mucosal surfaces.
Arrangements of bacterial flagelars
-Atrichous
-Monoatrichous
-amphitrichous
-Cephalotrichous
-Peritrichous
-Lophotrichous
extracellular enzymes is considered for what type of virulence factor?
-examples of some extracellular enzymes?
-what do these virulence factors do?
-example of a bacteria?
invasion (flagella, various toxins, enzymes)
Pathogens produce enzymes that break down host tissues and allow them to invade deeper into the body.
ECM enzymes
-Hyaluronidase
-Collagenase
-coagulase
-kinases
-catalase
Examples
Salmonella invading the microvilli of intestinal cells. After adhering to the microvilli with its fimbriae. It injects proteins into the cell disrupting the actin filaments and surrounding the bacteria to pull it inside. Once inside it becomes shielding w/n a vacuole and begins to grow. From here it can gain entrance to nearby tissues.
Streptococcus pyogenes produces hyaluronidase, which breaks down hyaluronic acid facilitating spread*
examples of some extracellular enzymes and what do they do?
ECM enzymes
-Hyaluronidase- allows bacteria to penetrate b/w cells. This will hydrolyze hyaluronic acid (intracellular cement)
-Collagenase - degrading CT
-coagulase - formation of fibrin clot (from fibrinogen). This will coat and protect the bacteria (walling-off process)
-kinases- degrade fibrin (dissolving clot) Expression of this enzyme is controlled by quorum sensing.
-catalase - degraded H202 into H20 and O2
Streptococcus pyogenes produces hyaluronidase, which breaks down hyaluronic acid penetrating b/w cells, then using collagenase to degrade the CT facilitating spread
Bacteria producing coagulase, and forming a clot. Then the bacteria producing kinase to dissolve clot and release bacteria.
Endotoxins are only found in what type of bacteria? Provide an example of a bacteria
Gram (-)
toxins composed of lipids that are part of the cell wall
Endotoxins: Lipid portions of LPS that are part of the outer membrane of the cell envelope of gram (-) bacteria (Lipid A). The endotoxins are liberated when the bacteria die and the cell wall lyses.
example
Salmonella Typhimurium
Exotoxins are found primarily in what type of bacteria? Provide an example of a bacteria
toxic substances released outside the cell
-proteins produced inside pathogenic bacteria, most commonly gram (+) bacteria, as part of their growth and metabolism. The exotoxins are then secreted into the surrounding medium during log phase.
example
Clostridium botulinum
Endotoxin and fever reaction
- Endotoxin (Lipid A of LPS)
- Leukocytes release cytokines
- TNF and IL-1 are released
- FEVER
- A macrophage ingests a gram (-) bacteria
- The bacteria gets degraded in a vacuole, releasing endotoxins that induce the macrophage to produce cytokines (IL-1, and TNG-alpha)
- The cytokines are released to the bloodstream by the macrophages, through which they travel to the hypothalamus (the temperature control center of the brain)
- The cytokines induce hypothalamus to produce prostaglandins to produce higher temperature = fever.
Which section of the LPS is embedded into the outer membrane of the bacteria?
Lipid A is embedded into the outer membrane, while the core polysaccharide and O polysaccharide are extended.