Dermatophytes & Malassezia

Question 1

Describe the colony characteristics of M. canis

Answer 1

white top surface
yellow/orange undersurface
flat w/ depressed center
cotton/wooly consistency

Question 2

Describe the macroconidia of M. canis

Answer 2

terminal knob
> 6 cells
thick cell walls
outer spines

Question 3

Describe the colony characteristics of M. gypseum

Answer 3

cinnamon brown top
tan undersurface
flat
powdery consistency

Question 4

Describe the macroconidia of M. gypseum

Answer 4

<6 cells

thin walls

Question 5

Describe the colony characteristics of T. mentagrophytes

Answer 5

white-cream top

tan undersurface

Question 6

Describe the microcondia of T. mentagrophytes

Answer 6

spiral hyphae

Question 7

Describe the colony characteristics of M. nanum

Answer 7

white to buff top
red-brown undersurface
downy-powdery consistency

Question 8

Describe the macroconidia of M. nanum

Answer 8

1-3 cells
pear-egg shape
numerous

Question 9

Describe the colony characteristics of T. rubrum

Answer 9

white top surface
red-brown under
downy

Question 10

Describe the macroconidia and microconidia of T. rubrum

Answer 10

macro: pencil-cigar shaped
micro: club-shaped to pyriform along hyphae

Question 11

Name the components of the DTM

Answer 11

1. Sabouraud’s dextrose agar
2. cycloheximide: anti-fungal
3. gentamicin: antibiotic
4. chlortetracycline: antibiotic
5. Phenol red: color change

Question 12

What is the color change seen in DTM w/ fungal growth?

Answer 12

Yellow–> red due to alkaline metabolites produced by dermatophytes

Question 13

What metabolite is responsible for fluorescence of M. canis under Wood’s lamp exam?

Answer 13

tryptophan (SAD?)

pteridine (Clinical consensus guidelines of dermatophytosis)

Question 14

What do you add to a horse DTM culture sample to grow T. equinum?

Answer 14

Vitamin B–> requires niacin for growth

Question 15

What do you add to a horse DTM culture sample to grow T. verrucosum?

Answer 15

Vitamin B–> requires thiamine for growth

Question 16

What is the wavelength of light involved in Wood’s lam examination?

Answer 16

253.7 nm (SAD)
360 nm (Clinical consensus guidelines of dermatophytosis)

Question 17

What are the ideal conditions for DTM culture?

Answer 17

30 degrees C and 30% humidity

Question 18

How often do you check DTM culture plates?

Answer 18

daily for growth AND color change up to 14 days

Question 19

What is a derm duet plate?

Answer 19

one side Sabouraud dextrose agar…may be easier to grow macroconidia

other side DTM

Question 20

Why is KOH more commonly used on human samples to evaluate for dermatophytosis than animal samples?

Answer 20

Human infections are more endothrix…need to remove keratin first w/ KOH

animal infections more ectothrix infection…spores on the outside of the hair shaft

Question 21

Which species of dermatophyte can cause reverse zoonosis?

Answer 21

Trichophyton rubrum

Question 22

What is the causative agent of athlete’s foot in people?

Answer 22

Trichophyton rubrum

Question 23

Name 3 treatment strategies for dermatophytosis in catteries or multi-cat households?

Answer 23

1. Total depopulation
2. Treat all animals
3. Treat kittens only

Question 24

How long can M. canis spores remain viable in the environment?

Answer 24

18-24 months

Question 25

Name the components of the fungal cell wall.

Answer 25

1. Mannoproteins 2. Beta 1-3 glucans 3. chitin 4. ergosterol

Question 26

What is the IHC gene for dermatophytes?

Answer 26

chitin synthase 1

Question 27

Which species of Malassezia is non-lipid dependent?

Answer 27

M. pachydermatis

Question 28

Which species of Malassezia are lipid dependent?

Answer 28

1. M. furfur 2. M. globosa 3. M. obtuse 4. M. restricta 5. M. slooffiae 6. M. sympodialis

Question 29

Which metabolite is responsible for the pigment change associated w/ Tinea versicolor?

Answer 29

azelaic acid metabolite--> inhibits tyrosinase--> hypopigmentation

Question 30

How does Malassezia adhere to the skin surface?

Answer 30

trypsin-sensitive protein adhesion

Question 31

Which types of neoplasia is generalized Malassezia dermatitis associated with?

Answer 31

1. pancreatitis cancer | 2. thymoma

Question 32

What other diseases are associated w/ generalized Malassezia dermatitis?

Answer 32

1. retroviral infection | 2. DM