Pathogenicity I Flashcards
what is pathogenicity?
Ability to cause disease
what is virulence?
Degree of pathogenicity
what is virulent bacteria?
Usually cause disease when they infect
what is virulence factor/gene?
Bacterial/component only involved in pathogenesis
what is the housekeeping gene?
Gene involved in all aspects of a bacterium’s life.
what is koch’s postulates?
- Pathogen occurs in every case of the disease and distribution corresponds to that of lesions observed.
- Pathogen does not occur in healthy subjects
- After isolation and repeated growth in pure culture, pathogen can induce disease in susceptible animals.
what is molecular koch’s postulates?
- Phenotype should be associated significantly more often with pathogenic organism than with non-pathogenic member or strain.
- Specific inactivation of gene(s) associated with the suspected virulence trait should lead to a measurable decrease in virulence.
- Restoration of full pathogenicity should accompany replacement of the mutated gene with the wild type original
what is virulent genes?
Often encoded on mobile genetic elements, bits of DNA that can be swapped between microbes.
where do virulence genes originate from?
Plasmids:
* adhesin genes – plasmid to bind more easily
* antibiotic resistance genes
* toxin genes
Bacteriophages: toxin genes
Pathogenicity islands convey a toxin gene systems
what factors define bacterial pathogenecity?
- Transmission – must be able to be transmitted to cause disease
- Adherence – once enter the host must be able to the target
- Invasiveness – sometimes, some pathogens can cause pathology without invading the underlying tissue. A lot of microbes need to invade.
- Ability to cause damage
how are microbes transmitted?
- Inhalation of pathogen
- Ingestion: Faecal contamination
- Inoculation:
* contaminated needles and blood transfusions
* skin contact
* insects
* sexual contact
how do microbes adhere?
- flagellae (also for motility) structures in their outer wall
- fimbriae (pili) structures in their outer wall
- specialised surface proteins: direct attachment or signalling to the eukaryotic cell to trigger further adhesion or even to encourage the eukaroytic cell to indigest the bacteria cell
Is adhesion always linked to virulence?
No, as long term commensals also adhere. However adhesion may affect virulence and tissue tropism (which particular tissue a microbe will infect).
how do bacteria interact with cells?
- Bacterium binds to eukaryotic surface through it fimbriae/pili. This then leads to a signal and a change in gene expression with the bacteria.
- Also induced signalling within the eukaryotic cell which leads to gene expression within that eukaryotic cell and production of compounds by the host cell.
- The compound could be either antimicrobial peptides or they could be markers which are involved in enabling further adhesion or uptake of the microbe by the eukaryotic cell.
what is colonisation?
Colonisation = Presence of microbes without accompanying disease
what is infection?
Infection = Presence of microbes resulting in disease critical colonization which lead to infection. This infection can be local or systemic.
how does microbe colonise ?
Colonisation happens through an attachment process.
why does microbes colonise?
A microbe would want to colonise a host for a source of nutrients:
* May receive nutrient from the waste products of the host
* More protected environment in the host
* soluble
* damage cells to obtain release
how does microbes survive?
- immune evasion - antigenic shift which is conducted by the Neisseria and Borrelia species
- oppose immune function eg superoxide dismutase, to inactivate immune cells
what properties aid microbe invasion?
Secreted bacterial enzymes
Antiphagocytic (protect themselves from pahgocytosis)
Toxins that control uptake mechanisms control
How do microbes enter the cell?
Phagocytosis - Induce uptake by macropinocytosis or endocytosis.
how do bacteria survive the conditions?
- Modifies the phagosomal compartment
- Escape the phagosome into the cytosol
- Nullify host response
how does chlamydia spread?
- Has a dimorphic life cycle exists in two forms. It starts if as a elementary body which is infectious but had no metabolism, it is metabolically inert.
- Attaches to cells and enters the cell.
- Once within the cell its triggers phagosome fusion. This phagosome fusion cause the reorganisation of the elementary body into a reticulate body.
- This reticulate body start to replicate it is not infectious so not capable of gaining entry into another cell however is metabolically active.
- Once it reaches a certain critically mass condensation of reticulate bodies into elementary bodies.
- Extrusion and release of infectious elementary body to infect other cells.
what is rickettsiae?
Obligate intracellular bacteria it is a Gram negative bacilli. This microbes replicates in the cytosol of host endothelial cells.
