MIIM - Pathogenesis of Infection - Week 1 Flashcards
Describe bacterial transformation.
When free DNA is taken up by a recipient bacterial cell and incorporated into its genome, this is known as transformation.
Describe transduction.
When a donor bacterial cell is infected with a bacteriophage, the bacterial DNA is incorporated into the bacteriophage genome.
When this bacteriophage infects another bacterial cell, the donor DNA is incorporated into the new bacterial cell genome. This is known as transduction.
Describe conjugation.
When pili connect two bacteria, a plasmif is transferred from one to the other.
Describe transposition.
A bacterial cell containing a plasmid with a transposon connects via a pilus to another bacteria. The plasmid is exchanged, and the new bacteria has the plasmid with the transposon incorporated into its genome.
Describe Koch’s 4 posulates.
- The microorganism must be present in every case of the disease
- The microorganism must be grown in a pure culture from the affected host
- Inoculation of the microorganism into a susceptible host should produce the same disease
- The microorganism must be recovered from the infected host
Name 3 limitations of Koch’s postulates.
- Normal microbiota is ineligible
- Fastidious bacteria cause problems
- No animal models for many human diseases
Describe Koch’s molecular postulates (4).
- The phenotype under investigation should be associated with pathogenic members of a genus/species
- The gene responsible for the disease symptoms should be found in all pathogenic strains, but not in non-pathogenic strains.
- Inactivation of the gene associated with the suspected virulence trait should lead to the loss of virulence
- Replacement of the mutated gene should restore virulence
Describe endogenous vs exogenous pathogens.
Endogenous - other sites on the host
Exogenous - other organisms (people, animals, plants)
Describe the 7 stages of infection. Specify which are symptomatic/asymptomatic.
Colonisation Invasion Replication Evasion of innate immunity Damage host Dissemination Immunity
The first 5 can be asymptomatic.
The last two are symptomatic.
What two factors affects the ability of bacteria to colonise?
Presence of adhesion receptors
A suitable microenvironment
What does epithelial colonisation depend on?
The interaction between ligands called adhesins, found on the microorganism surface, and specific receptoes on the epithelial cell surface.
Why may bacteria need to damage epithelial cells to gain access to receptors?
Epithelial cell are often polarised, so receptors may be differently expressed on different surfaces.
How do fimbriae assist in adhesion (4)?
Theyre short, rigid, and have a hollow core. The adhesin is on the tip.
Are non-fimbrial adhesions possible?
Yes, by using adhesins on their cell wall
What can a glycocalyx contribute to? Name 2 forms of a glycocalyx.
It can contribute to non-fimbrial adhesion.
Thet include capsules and slime layers.
Define quorum sensing.
Recognition by individual bacteria of chemical signals produced by a population of bacteria.
What happens to metabolic activity within biofilms?
It is reduced.
