bacterial pathogenesis Flashcards
1
Q
Local infection
A
- Entry of pathogen + multiplication at site
2
Q
Disseminated infection
A
- Entry of pathogen + multiplication + spread
3
Q
NM as opportunistic pathogens
A
- Change in circumstance / niche
○ Breach/injury at body surface, increase in numbers, altered immune status of host- Nosocomial infection
○ NM transferred to or between compromised individuals
- Nosocomial infection
4
Q
functions of virulence factors
A
- Enter host and colonise
- Adhesion via adhesins that are ligands for host cell receptor
- Invade and multiply host niches
- Cause cell damage
- Evade immune system - avoid phagocytosis (e.g. capsules), inflammatory response
- Cause damage via toxins and cytotoxic proteins, degradative enzymes
Resist antibiotics
5
Q
Genes for VF’s means of transfer
A
- Mostly on plasmids and bacteriophages
- Horizontal gene transfer
○ Plasmids
○ Bacteriophages
○ Transposons
Vf genes can be expressed together called pathogenicity islands
- Horizontal gene transfer
6
Q
HGT via plasmids
A
- Ds circular DNA
- Self replicating
- Encode for toxins, adhesins, invasion, drug resistance
- Transmitted via conjugation
If VFs absent on plasmids = no disease
7
Q
HGT via bacteriophages
A
- Virus infects bacteria
- Encode for toxins
Lysogenic phage integrates into the bacterial genome
- Encode for toxins
8
Q
HGT via Transposons
A
- Jumping genes
- Sections of DNA that can mover around in and out of the genome and between plasmids and bacteriophages
- Well known for transferring
○ Antibiotic resistance
○ Toxins
Pili
9
Q
Pathogenicity islands
A
- Large areas of chromosomal DNA that contain clusters of genes encoding VFs
Permanently integrated and dedicated to virulence
10
Q
how does virulence gene expression regulate
A
- To conserve energy
- Lack of nutrients, oxygen concentration, osmolarity, bile salts, temperature, antimicrobial compounds, oxidative stress
- Switch on and off
Regulated in response to population density = quorum sensing
11
Q
Updated Koch’s postulate
A
- The ‘virulence’ gene is always found in strains with a particular virulence phenotype
- The gene should be expressed in the host
- Mutation (inactivation) of that particular gene abolishes (reduces) the virulence phenotype
- Reintroduction of the gene reconstitutes the virulence phenotype
12
Q
portals of entry
A
○ Epithelial and mucosal membranes ○ Skin ○ Respiratory tract ○ Gastrointestinal tract ○ Urogenital tract Eye
13
Q
innate immunity
A
○ Physical barriers § shedding ○ Chemical and biochemical barriers § Secretions § Reflex response (sneeze, cough) pH
14
Q
colonisation
A
- Outcompete NM - biofilms
- Multiply
- Remain at site = localised
- May invade further
H. Pylori - Urease
○ Cleaves urea in stomach to produce ammonia which neutralise acid - Flagella
Creates motility driven by chemotaxis according to pH gradient
15
Q
adhesion
A
○ Contact with host cell - docking
○ Binding - specific - surface interactions
○ Mediated via adhesins - ligands that bind to complementary surfaces receptors on host cells