Micro: Fungal Infections

Question 1

Causative agent of Pityriasis versicolor

Answer 1

Malassezia furfur

Question 2

Component required for M. furfur to grow.

Answer 2

Long Chain fatty acids

-growth also stimulated by increased body temp, humidity, greasy skin, sweating

Question 3

Presentation of Pityriasis versicolor

Answer 3

Hypo or Hyperpigmented skin patches concentrated in regions with a high amount of sebaceous gland

Question 4

2 methods to diagnose Pityriasis versicolor

Answer 4

Woods Lamp: bright yellow fluorescence

KOH prep: unbranched hyphae w/ round spores (spaghetti and meatball appearance)

Question 5

Causative agent of Tinea nigra

Answer 5

Hortae werneckii

Question 6

Pathogenesis of Tinea nigra

Answer 6

Fungal cell growth of Hortae werneckii in the epidermis induces melanin production from melanocytes causing a brownish gray path on palms or soles

Question 7

Pathogenesis of White Piedra

Answer 7

Superficial infection of Trichosporon sp. causing white nodules to form on facial, axillary, and pubic hair.

Question 8

Complication of Trichosporon infection

Answer 8

Endocarditis (prosthetic or IV drug user vavles)

CNS infections

Question 9

Pathogenesis of Black Piedra

Answer 9

Superficial infection of Piedraia hortae. Forms an Ectothrix (black stone-like formation) on scalp and facial hair.

Question 10

3 causative agents of Dematophytoses.

Answer 10

AKA ringworm or Tineas

1. Trichophyton
2. Microsporum
3. Epidermophyton

Question 11

Presentation of the Dermatophytoses.

Answer 11

Athlete’s foot, jock itch, slap infection, nail infection
-lesions have a curved border and resemble a worm
(hyphae form in stratum corneum, deeper spread restricted by higher body temperature)

Question 12

Pathogenesis of Dermatophytoses

Answer 12

Fungus has keratinases (virulence factor) that degrades keratin and allows the fungal to grow and spread. A delayed hypersensitivity reaction induced by the host CMI causes inflammation and itching

Question 13

Most common cause of Tinea pedis, cruris (jock itch), corporis

Answer 13

Trichophyton rubrum

Question 14

How is Tinea cruris differentiated from Erythrasma?

Answer 14

Erythrasma fluoresces coral red and is caused by Corynebacterium minutissimum

T. cruris does not fluoresce

Question 15

How is Tinea cruris differentiated from Candida a.?

Answer 15

Candida affects the skin on the scrotum and thigh

Tinea cruris is mainly just the skin on the thigh adjacent to the scrotum

Question 16

Main causative agent of Tinea capitis

Answer 16

Trichopyton tonsurans

Microsporum can also cause it, differentiate with Wood Lamp

Question 17

Pathogenesis of Onychomycosis.

Answer 17

Fungal infection of the nail.

• caused by dermotophytes, Candida, some non-dermatophytes
• a secondary rash forms caused by a host inflammatory response

Question 18

Pathogennesis of Drunken Rose Gardener Disease

Answer 18

Break in the outer skin layers allows infection by Sporothrix schenkii

• the fungus infects local tissue causing papule formation
• eventually the fungus can spread by lymphatic channels forming a line of nodules and in IC patients it can disseminate thru the body.