Superficial, Cutaneous, and Sub-Cutaneous Mycoses Flashcards
What are the main components of the fungal cell wall?
Glucans, chitin, fibrillar proteins, mannoproteins, ergosterol
Name the different types of fungal morphology
Yeasts, molds, dimorphic
Name the 3 dimorphic fungi that you need to know
Histoplasma capsulatum, Blastomyces dermatitides, Coccidiodes immitis
What is the metabolism of a fungus?
Heterotrophs!
What are the three fungal pathways of infection?
Contact, trauma, inhalation
Type I Hypersensitivity
Allergic Rhinitis
Type III Hypersensitivity
Farmer’s Lung
What does a wet mount with 10% KOH do?
Kills everything except for the fungi
What does staining with Lactophenol Cotton Blue accomplish?
Determines if the fungi are septate or aseptate
What does Sabouraud’s Agar accomplish?
Suppresses non-pathogenic fungi
What is serology used for?
Deep or systemic infections
Polyenes
Amphotericin B (oral) and Nystatin (topical)
Mode of Action: Binds ergosterol and forms pores in fungal cell membranes
Resistance: Reduce amount of ergosterol or replace ergosterol with fecosterol
Flucytosine (5-Fluorocytosine)
-Converted to 5-FU by cytosine deaminase and brought into the cell via permease
-MOA: Competes with uracil to block RNA synthesis and 5-FUMP interferes with thymidylate synthase to block DNA synthesis
Resistance: Block cytosine deaminase and permease
What are the two types of azoles?
Imidiazoles: Ketoconazole and Miconazole
Triazoles: Fluconazole, Itraconazole, Voriconazole
Azoles (MOA &Resistance)
MOA: Inhibits 14-alpha demethylase which converts lanosterol to ergosterol (lano is toxic)
Resistance: Alter 14-alpha demethylase or efflux drugs out of the cell faster than they come in
Echinocandins
MOA: Interfere with beta 1,3 glucans
Resistance: Target alteration
Allylamines
MOA: Inhibits squalene epoxidase needed to make ergosterol
***Works very well for skin infections
Resistance: Efflux from cells
Who is Griseofulvin prescribed for?
Given orally for kids with ringworm. Messes with mitosis
What does Tolnaftate due?
Inhibits squalene epoxidase (A Allymine)
What is Tinea Versicolor caused by?
Malassezia furfur
What can Tinea Versicolor cause?
Seborrheic dermatitis (actually itches unlike original condition)
How do you diagnose Tinea Versicolor?
1) Spaghetti and meatballs appearance on KOH
2) Fluoresces yellow under Wood’s lamp
3) Culture on mycologic agar&olive oil
What is White Piedra caused by?
Trichosporon Cutaneum
Does White Piedra damage the hair?
No
What is a characteristic of White Piedra?
Grows well on Sabouraud’s agar
How would you treat White Piedra?
Topical azoles
What are the three organisms that cause Cutaneous Mycoses (Dermatophytoses)?
1) Trichophyton
2) Epidermophyton
3) Microsporum
What are the four species of Trichophyton?
1) Rubrum
2) Mentagorophytes
3) Tonsurans
4) Verrucosum
What are some characteristics of Trichophyton?
May see spiral hyphae. Microscopically identified by their condida. Macrocondida are rare.
What are some characteristics of Epidermophyton?
Macroconidia are smooth-walled and in cluster. Microcondidia are rare. Does not infect hair!
What are the three species of Microsporum?
1) Canis
2) Gypseum
3) Fulvum
What are some characteristics of Microsporum?
Macroconidia are large, rough, and thick walled. Microconidia are rare. Does not infect nails!
What two organisms cause Tinea Corporis (ring worm)?
T. rubrum (anthropomorphic) and M. canis (zoophilic)
What is the most common Dermatophyte?
Tinea Pedis (Athlete's Foot) -Can progress to the toenail
Describe a major characteristic of Tinea Cruris (jock itch)
It does not affect the scrotum!
Ectothrix
Microsporum. Grows outside of hair shaft.
Endothrix
Trichophyton. Grows inside of hair shaft.
Describe the characteristics of Tinea Capitis and Barbae
Live off of the hair shaft unlike T. cutaneum
- Dull grey patches of alopecia, scaling, and itching
- Kerion may form in response to infection with zoophilic dermatophyte
Tinea Unguium
Caused by T. rubrum but can be caused by other organsims
-Nails become thickened, discolored, friable, deformed
How would you diagnose a Dermatophytosis?
- KOH preps
- Microsporum grows under Wood’s lamp
- Endothrix vs. Ectothrix
- Inoculate on Sabouraud’s agar
How would you treat a Dermatophytosis?
1) Topical azoles work very well
2) Oral azoles
3) Terbinafine (oral&topical)
4) Partial surgical removal of nails
Where do the organisms that cause a subcutaneous mycosis live?
Soil and vegetation
What does a subcutaneous mycosis require in order to bypass intact skin?
Trauma
What is the typical course of a subcutaneous mycosis?
Chronic and insidious
What is Lymphocutaneous Sporotrichosis caused by?
Sporothrix schenckii
Describe the morphology of Lymphocutaneous Sporotrichosis
At ambient temp it’s got septate hyphae and conidia arranged in a flower pattern with thin conidiophores
At body temp its a pleomorphic yeast
What is Lymphocutaneous Sporotrichosis associated with?
- Warm climates (Japan, N and S America)
- Associated with trauma (rose thorns)
- Also associated with armadillos and cats
Describe the pathogenesis of Sporotrichosis
- Primary lesion is a small ulcerating lesion
- Secondary lesions are subcutaneous nodules that appear two weeks later and follow lymphatic drainage
What is fixed Sporotrichosis?
- Occurs in Mexico
- A single non-lymphangitic nodule
How would you diagnose Sporotrichosis?
-Culture pus from ulcerated nodule or infected tissue
How would you treat Sporotrichosis?
- Oral Itraconazole is the current drug of choice
- Classic treatment was oral KI
