Mycology

Question 1

a) define mycoses

b) What are the four principle types of mycoses?

Answer 1

a) mycoses: fungal infections of body
b) • Superficial and cutaneous mycoses: Keratin (hair, skin, nails) and mucous membranes
• Subcutaneous: Dermis, tiss, bone
• Systemic: Internal organs (esp lungs)
• Opportunistic: infections in immunocompromised (young, elderly & sick) => result in above mycoses

Question 2

What general growth conditions do fungi prefer?

Answer 2

• moist (incubate in dark chambers)
• low pH
• High [glucose]
• 20-28ºC

Question 3

List two disadvantages or problems associated with antifungal drug therapy? How are patients monitored?

Answer 3

• treatment is usually long term

- toxicity (bc dealing w/ eukaryotic organisms- same as us)=> must have regular FBC (blood), LFT (liver) & RFT (renal)

Question 4

Why are samples of skin, hair or nails treated with 10-20% KOH? (3)

Answer 4

• Clears keratin
• Separate cells
• Helps detection and examination

Question 5

a) What is the common component of hair, skin and nails that the Dermatophyte fungi invade/require for growth? b) Which genera use which?

Answer 5

a) Keratin
b) - Trichophyton sp.: nails, skin, hair
- Epidermophyton sp. : nails, skin
- Microsporum sp.: skin, hair (M.canis: pets, animals)

Question 6

What are coencytic hyphae?

Answer 6

Aseptate hyphae (continous hypahe contaning spores)

Question 7

In a typical mould, what is the name of the segment of hyphae from which spores grow?

Answer 7

Septate (segmented hyphae containing spores)

Question 8

In a mould that produces a spore sac (sporangium), what is the name of the segment of hyphae from which the sac grows?

Answer 8

Sporangiophore (-phore: “bearing”/ to bear)

Question 9

Why do culture media for the isolation of fungi and yeast often contain a chemical agent such as Chloramphenicol or Cycloheximide?

Answer 9

Kills bact @ toxic [ ] = allow mould & yeast to grow

Question 10

What group/type of people would be considered to be immunocompromised?

Answer 10

• Elderly
• young
• sick: immune disorders - AIDS or following chemo

Question 11

Why are the lungs, the primary site of infection for many fungal diseases?

Answer 11

Spores are in the air & easily to inhale it

Question 12

Which organism is primarily associated with fungal meningitis in the immunocompromised?*

Answer 12

Cryptococcus neoformans

Candida sp.

Question 13

What test is characteristically positive for Candida albicans? How is the test performed and what denotes a positive result?

Answer 13

Germ tube test:

1. incubate yeast colony in horse/human serum @ 37ºC for <2hrs (prolonged time hard to identify w/ other Candida sp)
2. Pos: tube-like projection from yeast cell (true hyphae)

Question 14

What colony feature (if present/seen) is characteristic of C.albicans?

Answer 14

BA: Starburst colonies (small filaments growing out of yeast colony) but not always see
Chromogenic media: green colony

Question 15

What are the types of fungi?

Answer 15

1. Moulds: multicellular filamentous colonies (fluffy)
2. Yeasts & yeast-like fungi: single cells -> colonies
3. Dimorphic fungi: can grow like moulds/filamentous (room) or yeast/colony (37ºC) depending on temp.

Question 16

What is the difference between pseudohyphae and true hyphae?

Answer 16

True: parallel sides w/ no constrictions
Pseudo: sausage-like constrictions

Question 17

a) Which one of the dimorphic fungi does not start as lung infection?
b) Usual treatment
c) what type of mycoses does all dimorphic fungi cause

Answer 17

a) Sporothrix schenckii
b) self-limiting (no treatment) depending on size of inoculum
c) Systemic infections, esp immunocompromised

Question 18

How is the role of fungal spore different to bacterial spore?

Answer 18

Fungal spore: for fungal (a/sexual) reproduction
Bact. spore: survival of the bact. when conditions are unfavourable to live in, & can withstand harsh conditions => germinate once condition becomes favourable

Question 19

Why is sputum collected early in the morning?

Answer 19

• easy to collect bc sputum build up overnight

- food can have yeast & spores (interfere)

Question 20

What is the difference between aerial hyphae and vegetative mycelium (hyphae network)?

Answer 20

• Ariel: give rise to repro. spores on surface

- Vegetative: nutrient absorbing & H2O exchange under media/tissue

Question 21

name 4-7 dermatophyte infections (ring worm & tinea) and state what superficial areas is affected

Answer 21

• Tinea capitis: skin & hair
• Tinea corporis: trunk, limbs & extremities
• Tinea cruris: groin & pubic area
• Tinea pedis: feet
• Tinea manuum: hands
• Tinea unguium: finger nails & toe nails
• Tinea barbae: beard

Question 22

Lab features of Cryptococcus neoformans

Answer 22

• Large capsule (demo w/ India ink wet prep)
• Mucoid colonies
• Bird seed agar: brown
• Urea: pos
• Use latex agglutination to detect genus
• S to cyclohexamide

Question 23

Colour of Candida albicans when grown on chromogenic media (@42-45ºC)

Answer 23

green

Question 24

Distinduish b/w following asexual conidia/conidiospores

• Arthospores/arthoconidia
• Blastospores/blastoconidia
• Chlamydiospores/chlamydoconidia
• Microconidia vs. macroconidia (-spore)
• Sporangiospores

Answer 24

• Artho: spores within hyphael segments
• Blasto: budding yeast cells
• Chlamydio: thick walled resting spores
• Micro: little single-celled spore
• Macro: lrg multicellular spore
• Sporangio: spores held w/in a sack (sporangium)