Lecture 5 - Medical Mycology

Question 1

Human mycoses can be classified based on the location of the disease. Mention all of them and give examples.

Answer 1

Superficial:
- Caused by dermatophytes
- Exp. Tinea pedis (athlete's foot)
Subcutaneous:
- Wound and mucosa layer infections
-Exp. Candida albicans -> thrush

Systemic Infections:

• enters as spores and spreads
• Exp. Cryptococcus sp.

Question 2

Differ between invasive opportunists and primary pathogens in the context of systemic infection.

Answer 2

Invasive opportunists are mycoses that ONLY affects immuno-compromised individuals. Primary pathogen causes systemin infection in healthy individual as well, given high dose.

Question 3

A strong immune response to an infection does not necessarily beneficial to the patient. Explain this concept in the context of Aspergillus fumigatus.

Answer 3

To fight an infection, the response of the immune system must be adequate, not too low nor too much. In the case of A. fumigatus, a weak response would lead to systemic aspergillosis, allowing fungus to grow in tissues due to a suppressed immune system. On the other hand, a strong response such as the case in Farmer’s lung, where spores trigger a massive allergic reaction, is not good either.

Question 4

Why are fungal diseases difficult to treat?

Answer 4

Since fungi are eukaryotes and a close relative to animals, most antifungals can also have a detrimental affect to human cells and tissues due to the same composition and structure. Emergence of drug resistant strains also play a role.

Question 5

Mention five anti-fungal substances and their function.

Answer 5

Griseofulvin: Inhibit microtubule production -> inhibit mitosis

Echinocandin: Inhibit glucan synthesis (cell wall)

Azoles: Inhibit ergosterol biosynthesis pathway

Flucytosine: Inhibit DNA replication

Polyene: binds to ergosterol (membrane), disrupts membrane integrity

Question 6

Describe the disease ergotism.

Answer 6

It is disease caused by the consumption alkaloids produced by the Claviceps purpurea fungi. Toxic alkaloids include ergotamine (vasoconstrictor), LSD, ergotamine, etc.