Types of mycoses

Question 1

What is onychomycosis?

Answer 1

a fungal infection of the fingernails or toenails =>discoloration, thickening, and separation of nail from the nail bed

Question 2

How could you differentiate between the other two genera of dermatophytes that have ‘thick walled’ macroconidia?

Answer 2

Microsporum: 5+ septa, w/ rough wall
Epidermophyton: <=4 septa, pear-oval shaped

Question 3

Which agar would encourage the formation of pseudohyphae by yeast?

Answer 3

Cornmeal & Tween 80 agar

Question 4

Infection sites of Candidiasis

Answer 4

• mucocutaneous
• cutaneous
• systemic

Question 5

Tests/agars that help in yeast ID

Answer 5

• germ tube
• Biochemical rxns: Chromagar, API ID32C
• Bird seed agar (for Cryptococcus neoformans)
• Cornmeal + tween 80 agar (for growing pseudo/true hyphae

Question 6

Compare & contrast superficial mycoses, Cutaneous mycosis & dermatophytosis

Answer 6

Both: Superficial infections of hair, skin, nails i.e. no living tissue invaded
Superficial: Innocous (asymptomatic, no itch), stratum corneum
Cutaneous: hair, skin, nails
Derma: use keratin for nutrients

Question 7

Pityriasis versicolor

a) type of mycoses it causes
b) Organism responsible

Answer 7

a) superficial mycoses (on trunk, shoulder, arms)

b) Malassezia furfur

Question 8

a) Name two genera within the mucormycotina that can cause systemic infection?
b) Which genus is the most common cause of human fungal infections?
c) treatment recommended

Answer 8

a) Rhizopus sp, Apophysomyces sp, (Sporothrix sp.)
b) (Sporothrix sp)
c) Treatment usually requires a dual approach with surgical excision and Amphotericin B

Question 9

Which genus is the second most common cause of human fungal infections?

Answer 9

Aspergillosis

Question 10

What criteria is used to confirm whether Aspergillus is actually causing an infection or is an environmental contaminate?

Answer 10

Must see mycelium in direct microscopy to confirm infection

Question 11

a) difference of uniserate & biserate

b) give E.g of Aspergillus sp for each

Answer 11

Uni: phialides directly from vesicle e.g. A.fumigatus
Bi: philaides from metulae - connects to vesicle e.g. A.niger, A.flavus, A.nidulans

Question 12

Which form of a dimorphic fungus is most pathogenic?

Answer 12

yeast?

Question 13

Which one of the dimorphic fungi is most frequently isolated in Australia? Describe it’s microscopic appearance at RT and at 37˚C? What ‘text book’ shape are the yeast cells when they exist in pairs and are seen in clinical samples?

Answer 13

Histoplasma capsulatum
Mould: Top: white suede, bottom: yellow-brown
Microsc: round single-cell macroconidia, septate hyphae

Question 14

Which dimorphic fungus is endemic in the Americas and is characterised by the
formation of arthroconidia in its mycelial phase?

Answer 14

Coccidoides immmitis

Question 15

Which former species of Penicillium is a considered a true pathogen?

Answer 15

Talaromyces (penicillium) marneffei

Question 16

What’s the ID process of yeasts

Answer 16

• Combo of morphological features & biochemical test
• Encapsulated yeast => ID sp.
• All yeast from sterile body fluid/tissue => ID sp.
• Chronic or recurrent infection => ID sp

Question 17

How bird seed agar makes Cryptococcus neoformans & C. gatti turn dark brown

Answer 17

Colony produce pheno oxidase = breakdown melanin in agar => dark brown