Mycology

Question 1

Fungi

Answer 1

Mycosis - fungal infection

Eukaryotes, chitin cell wall, most multicellular (yeasts are unicellular), no chlorophyll, non-motile, spores are obligate aerobes

Grow in the form of branching filaments called hyphae. Hyphae may be separate (lots of cells) or merge together to form a mycelium.

Question 2

Fungi reproduction

Answer 2

Asexual - mitosis/binary fission, production of spores and budding

Sexual - meiosis, haploid nuclei fuse through hyphae touching

Question 3

Fungi food source

Answer 3

Saprotrophic - feed on decaying matter
Parasitic - feed on living matter

Some form mutualistic relationships e.g. Cyanobacteria and lichens

Question 4

4 types of fungal diseases

Answer 4

Superficial (skin, hair, nails)

Subcutaneous (under skin) - usually occurs in tropical environment where people walk bare-foot. Cuts allow invasion of fungal disease

Invasive/systemic - very rare, usually affects lungs, high mortality

Mycotoxicosis - causes immunosuppression or carcinogenesis e.g. Aflatoxins (B1 most toxic)

Question 5

Causes of superficial diseases

Answer 5

Two main causes are :

DERMATOPHYTES:
Trichophyton - most common, athletes foot (Tinea pedis) scalp ringworm (Tinea capitas)
Microsporium - mostly held in animals, ringworm in pets, tinea capitis/corporis in humans
Epidermophyton - ringworm

and CANDIDA ALBICANS

Question 6

Ringworm

Answer 6

Superficial

Circular areas of baldness (alopecia) and crusting around head, arms.

Dermatophytes infect hair follicles and surrounding skin

Hairs can break off and still be infective in the environment for months

Question 7

Mucosal membrane infections - Thrush

Pathogen, risk factors, virulence, symptoms, treatment

Answer 7

Superficial (tongue)

Pathogen: Candida albicans - CANDIDIASIS
Risk factors: diabetes, age, cuts, antibiotic use, obesity
Virulence: surface integrins (adhesion), proteases, phospholipases, biofilm
Symptoms: white tongue, difficulty swallowing, soreness
Treatment: antifungal - nystatin

Question 8

Lab methods for fungi

Gram stain, Agar

Answer 8

Gram stain black

Sabouraud Dextrose Agar is a classic medium. Add chloramphenicol to inhibit bacterial growth.

Question 9

Treatments for fungal diseases

Answer 9

Nystatin - Oral or topical for Candida

Imidazole (topical) or triazoles (oral) - prevents production of ergosterol so fungi can’t reproduce

Itraconazoles - treats invasive infections including candidiasis

Caspofungin - inhibits synthesis of glucan in cell wall for Candida

Griesfulvin - oral used to treat dermatophytes