introduction to fungi

Question 1

Explain the classification and structure of fungi.

Answer 1

Fungi are chemo-oragno trophic eukaryotes which lack chlorophyll and produce spores. Their cell wall contains polysaccharides (glucan and chitin)and absorbs nutrients. Their membrane contains ergosterol as the main source of sterol.
Fungi are classified according to their morphology into: mushrooms, yeasts, moulds.
Based on biochemical properties:
Basidomycete - mainly moulds and mushrooms
Zygomycete- more than one spore in a rough wall -mainly moulds and yeast
Ascomycete- spores contained in sacs- only moulds
Asexual spores:
-Basidiomycete- conidium
-ascomycete: conidium
-Zygomycete: sporagiospore

Question 2

Describe the clinically important systemic and dermatophytic fungal infections.

Answer 2

Dermatological:
-Dermatophycetes- moulds which break down keratin and use it as a source of nutrient. Ring-worm infections.
-Athlets foot
-thrush
-pityriasis infection
Systemic:
-Candida ( Albicans, Tropicalis): Infect deep organs of patients with compromised immune systems. They are commensal yeasts in the GI tract. They can cause superficial infections ( nails, skin, penis, vagina, mouth) or disseminated.
-Aspergillus ( Flavus, Fumigans): Infect deep organs of patients who are undergoing chemotherapy. They are moulds. They are highly angioinvasive. They are ingested through their condida. Main diseases: asthma and aspergilloma

Question 3

Describe the host factors that contribute to the pathogenicity of fungal infections

Answer 3

• Warm/ moist environment- allows the growth of fungi on skin and mucosal membranes
• Immunocompromised immune system
• Broad-spread antibacterials- reduce competition for epithelium in GI tract

Question 4

Describe the diagnostic methods for detecting fungi

Answer 4

• Direct ( smear test, High res CT scan, histopathology)
• Antigens for fungi
• Antibodies for fungi
• Growth of culture from a usually sterile site
• PCR for fungal DNA

Question 5

Describe the mechanisms of action of anti-fungal drugs, their route of administration and issues associated with anti-fungal agents

Answer 5

Issues:
-cost
-IV/Oral
-specificity of drug
-resistance
-toxicity
Types:
-Echinocardins- target wall-glucan- IV
-Polyenes -target membrane 
-Triazoles and allylamines- target sterols- IV, topical and oral
-Flucytosine- targets DNA synthesis