Pathogens Flashcards
Categories of disease
Infectious disease:
* Result from the pathogen’s growth
Intoxications:
* Result from the presence of a specific toxin
Pathogen
Microbial parasites that are able to cause infection
* identified by the set of virulence genes that are carried and expressed
Infection
Situation where microorganism is established & growing in host, causing damage
Disease
Damage/injury to the host that impairs host function
Pathenogenicity
Ability of a parasite to inflict damage to the host
Virulence
Measure of pathogenicity
Opportunistic pathogen
Cause disease only in absence of normal host resistance
Virulence
Measure of the ability to cause damage
Determined by 2 features:
* Invasiveness
* Toxigenicity
Invasiveness
Ability to become established, overcome defenses, & spread in tissues
Invasiveness Virulence factors
- Adhesins
- Capsule
- Enzymes that destroy host tissues
- Invasins
- Type 3/4 Secretion Systems
Adhesins
Promote specific attachment to the host cell surfaces
* Fimbriae/pili mediate loose attachment
* Afimbrial adhesins mediate close attachment
Capsule
Prevents pathogen from being destroyed by host immune cells
Enzymes that destroy host tissues
Hyaluronidase:
* Degrades hyaluronic acid (holds host cells together)
Collagenase:
* Degrades the protein collagen present in connective tissues
Lecithinase:
* Degrades lecithin in cell membrane
* Lysis of RBCs and tissue cells
Hemolysins:
* Enzymes and cytolysins (pore-forming)
* Cause RBC & tissue lysis
Invasins
Surface/injected proteins that allow microorganisms to enter cells
Type 3/4 Secretion Systems
- Invasion of host cells
- Block phagosome maturation
- Take control of host cells
Toxigenicity
Capacity to produce toxins that damage specific tissues of the host
Toxin categories
- Exotoxins
- Endotoxins
Exotoxins
- Secreted into the surrounding as the bacterial pathogen grows
- Highly antigenic
- Heat-labile
- Usually proteins
- Categorized by their target
Exotoxins examples
- Extracellular enzymes: Degrade host cells
- AB toxins: Modify host cells
AB toxins
Subunit A:
* modifies target inside host cell leading to damage to the host
Subunit B:
* binds specific cell receptors providing tissue/cell type specificity
AB Toxins: Cholera toxin
Subunit A:
* adenylate cyclase, produce cAMP
Subunit B:
* bind to intestinal cells
Endotoxins
- Part of the bacterial pathogen
- Weakly antigenic
- Heat-stable
- Very effective activator of the immune system
- Produce general systemic effects (fever, inflammation)
Vaccines against toxins
Exotoxins
* Toxins inactivated to toxoids by heat/formaldehyde
* Toxoids are no longer toxic, but still antigenic
Endotoxins:
* Cannot be inactivated to toxoids – no vaccines
