Fungal Pathogens II Flashcards
Damage from disease can occur in 2 ways
- Direct damage from microorganism (e.g. not enough host response)
- Damage from host immune over-reaction
Damage to the host will have a
Disease threshold
Candida infection can cause both
Direct damage (systemic infection) Host overreaction (cutaneous infection)
Identification of virulence factors
Reverse genetics - candidate gene approach (most common) ‘is this gene important in virulence?’
Forward genetics - genome wide approach
Confirmation of virulence factors
Koch’s molecular postulates
- Disrupt target gene to create mutant strain
- Demonstrate attenuated virulence of mutant
- Reintroduce gene to restore virulence
The status of the host is very important in
Candida infection
Stages of candida infection
- Adhesion and colonisation
- Epithelial penetration
- Vascular dissemination
- Endothelial colonisation and penetration
C albicans virulence is
Multi factorial
Candida virulence factors
- Adhesion to host surfaces
- Invasion of epithelial layers
- Penetration beyond epithelia
- Obtaining nutrients
- Opposing host defences
Host defences
- Flushing mechanisms
- Molecular recognition
- Phagocytosis and killing
- Immune response
Characteristics of candida
- Diploid (8 chromosomes)
- Largely asexual
- Polymorphic
- CUG codon
- Causes candidosis
C albicans polymorphisms
- Yeast
- Pseudohyphae
- Hyphae
- Opaque
- Chlamydospore
What causes hyphal growth
High temps above 35 Neutral pH 6.5 High pCO2 low pO2 N/C starvation Matrix embedded growth
What causes yeast growth
Low temps below 35
Acidic pH
Nutritious environment NH4+ ions
What also plays a role in morphogensis between yeast and hyphae?
Quorum sensing
Quorum sensing tells candida in high cell densities
To grow as a yeast