Fungal Pathogens Flashcards
(55 cards)
What are yeasts?
Unicellular oval shaped fungi
What are moulds?
Typically multicellular fungi that form a network of thread-like structures called hyphae.
What are 2 examples of yeasts?
Candida spp. (generally)
Cryptococcus spp.
What are 2 examples of moulds?
Aspergillus spp.
Mucor spp.
What is the name for a fungi that can switch between yeast and mould?
Dimorphic fungi
What are 2 examples of dimorphic fungi?
Histoplasma
Candida albicans
Why are fungi clinically important?
- 1.5 million deaths/year (WHO 2023); comparable or exceeding deaths from malaria or TB
- Emerging threats like Candida auris and Aspergillus fumigatus
What causes dimorphic fungi to change morphology?
Primarily temperature, but other factors like pH and nutrient availability can also induce change
Generally, what temperatures induce are dimorphic fungi yeast, and mould?
Yeast - 37C (human body temp)
Mould - 25C (room temp)
How do yeasts and moulds grow respectively?
Yeasts - budding
Moulds - apical extension
What is something that in unique to fungal pathogens that makes it difficult to find effective antifungals?
As eukaryotic pathogens, they share many similarities with host cells, making the development of effective and safe anti fungals difficult
What percentage of global infectious disease funding do fungal pathogens receive?
Less than 1.5%
What is morphological switching in Candida albicans and why is it important?
The ability to switch between yeast and hyphal forms. Hyphae penetrate tissues and escape phagocytosis, enhancing virulence.
Do moulds like Aspergillus fumigatus undergo morphological switching?
No — they grow as filamentous hyphae. Their virulence depends on other factors like spore formation and toxin production.
Which fungi produce toxins and what do these toxins do?
Moulds like Aspergillus produce gliotoxin, which suppresses the immune system by:
- Inhibiting neutrophil function
- Inducing host cell apoptosis
- Blocking reactive oxygen species (ROS) production
What are the main virulence factors used by Candida spp.?
Morphological switching (C. albicans)
Adhesins
Biofilm formation
Release of hydrolytic enzymes
Phenotypic switching
B-glucan masking
What are the main virulence factors used by Aspergillus spp.?
Spore formation
Gliotoxin production
Release of hydrolytic enzymes
Biofilm formation
What are the main virulence factors used by Cryptococcus spp.?
Polysaccharide capsule
Melanin production
Titan cell formation
Phenotypic switching
CNS tropism
What are Candida adhesins?
Fungal surface Als proteins. Important for:
- Adhesion to epithelial and endothelial cells (colonisation), as well as abiotic surfaces (e.g. catheters)
- Formation of biofilms
What enzymes does Candida secrete, and what do they do?
Hydrolytic enzymes like:
- Aspartyl proteases (degrade immune molecules)
- Phospholipases (disrupts host cell membranes; facilitates invasion)
What enzymes does Aspergillus secrete, and what do they do?
Hydrolytic enzymes like:
- Proteases and elastases, which degrade host extracellular matrix (e.g. elastin in lung tissue)
- Aids in lung and blood vessel colonisation
What are the spores formed by Aspergillus?
Spores are called Conidia, and they are a key way in which Aspergillus can spread:
- Tiny in size (allow to bypass upper respiratory defences straight to alveoli)
- Surface rodlet proteins + melanin protect against immune defences
- Once in host lung, they can germinate into hyphae; allow for invasion of tissue
What is the Cryptococcus polysaccharide capsule?
A polysaccharide outer layer that protects from phagocytosis and aids in immune evasion
What is the role of melanin production by Cryptococcus spp.?
Melanin works to neutralise reactive oxygen species, protecting the fungi from oxidative damage
