5. Medical Mycology Flashcards
Why do only few species cause diseases in mammals?
- Our immune system is effective
- Grow slowly under low oxygen
- few are capable of growth at 37 degrees
What are some examples of skin, hair or nail diseases causes by fungi?
- Dandruff
- Athlete’s foot
- Toe nail fungus
What fungus group causes superficial infections?
Dermatophytes cause ringworm, tinea
What is the mode of infection for superficial infections of fungi?
- Keratinolytic
- Enzymes for breaking down keratin, specialised to these fungi which attach onto the skin
What are subcutaneous infections?
- Usually those from wounding in which the skin surface layer is damaged
- Infection spreads through the lymph system
Which fungus phylum is the one responsible for causing invasive fungal infections?
Microsporidia of phylum microspora
What do the microsporidia lack?
Lack normal mitochondria and have no flagella, making them obligate intracellular parasites
What is the spore wall structure of microsporidia?
Spore wall is made of chitin (same as fungal wall) and stains with Calcofluor white
What is the life cycle of microsporidia?
- Spores are ingested from the environment
- They invade host cells by everting structures known as polar tubes
- The sporoplasm (parasite cell without wall) is injected through the tube into the host cell
- Replication then spores released
What is Candida albicans and what does it cause?
- C. Albicans is a normal part of most people’s microflora
- Causes thrush, vaginitis, and in rare cases systemic disease
What is one virulence property of C. Albicans?
The ability to switch between yeast and hyphal growth
What is dimorphic switching?
Transitions between yeast and hyphal forms of growth in Candida
What are the three stages of dimorphic switching in Candida?
Budding system, intermediary pseudohyphal stage, filamentous stage
What is the yeast and hyphal stage of candida each most important for?
- Yeast form more important for spreading around the body
- Filamentous form is the one for escaping tissues and macrophages
Where do symptoms of C. Albicans infections arise from?
Symptoms develop if bacterial competitors in the natural microflora are disrupted.
- Through antibiotics, during pregnancy (elevated progesterone), stress, abrasion
How does dimorphic switching work in other Candida fungi (not c. Albicans)?
Grow as yeast at human body temperature (pathogenic) and as hyphae in the environment
What is the infection pathway of cryptococcus spp?
- Bird excretions contain amoeba which affect eucalyptus trees
- Spores inhaled into lungs
- Lodge in alveoli
- Dissemination to central nervous system
- Positive culture test shows melanin positive and capsule positive
What are some properties of aspergillus fumigatus?
- Found everywhere (especially compost)
- High spore production
- Resists high temperatures
What is systemic aspergillosis?
An organ transplant patient may have a suppressed immune system so the fungus grows in tissue
What is Farmer’s lung?
Inhalation of large numbers of spores, where an overly strong immune system induces an allergic reaction
What are so few fungicide classes available in medicine?
- Fungi are difficult to treat because they don’t have much unique biochemistry due to being eukaryotes and close relatives of animals
- Many antifungals have severe side effects
What are azoles?
Fungicides which target Erg11 for the synthesis of ergosterol
- Ergosterol is similar to cholesterol
- Erg 11 is the enzyme that produces ergosterol
What are echinocandins?
Fungicides which target Fks1
- Fks1 is the enzyme required for 1,3 beta glucan synthesis of the fungal cell wall
What 2 physical syndromes do claviceps purpea cause?
- Gangrenous ergotism (fatigue, prickles, inflammation, gangrene)
- Convulsive ergotism (cramps, convulsions)
