Derm Fungi Flashcards
What is the most common dermatophyte fungus?
Trichophyton rubrum
What is the causal agent behind Tinea nigra?
Hortae werneckii
What is the most important virulence factor of the tineas?
keratinases to get through the stratum corneum
Which mycetoma granules are black?
M. grisea and E. jeanselmei
Why is tinea versicolor a misnomer for pityriasis versicolor?
Tinea describes ringworm type infections, Malassezia furfur is NOT a ringworm
What is unique of the cell walls of Hortae werneckii?
They are melanized, it is a dematiaceous fungus
Where do most of the subcutaneous mycoses come from?
soil
Who would be most at risk of a dermatophyte becoming a chronic issue?
Can happen in anyone but HIV and IC
What 3 bugs should be on the differential for “jock itch”?
Erythrasma = Corynebacterium minutissimum; Tinea cruis, and candida
Where is the most likely location of hyphae in a tinea infection?
Stratum corneum; these are dermatophytes
Which dermatophytoses are most common in A) Men and B) Women?
A) tinea capitis, tinea pedis, and tinea cruis B) tinea unguinum
What does Malassezia furfur look like on Wood’s lamp? On KOH?
Wood’s lamp = fluoresce bright yellow; KOH = spaghetti and meatballs
How does Sporothrix spread?
along the chain of lymphatics
Which causal agent of a mycetoma may disseminate in HIV or IC pts?
P. boydii (white granules)
When a person has a mycetoma, which two organisms are most likely to cause a superinfection?
staph and strep (NF of the skin = most likely)
T/F: both Piedraia hortae and Hortae werneckii are dematiaceous fungi?
True these are black piedra and tinea nigra, respectively
What kind of systemic infections can Trichosporon cause? What enzyme is it positive for in the lab?
Endocarditis of prosthetic valve or on native valve if IVDU; urease
How do you get Sporothrix schencki? What area of the body is most commonly involved?
Usually from a thorn prick, often the hands
How do you get a chromoblastomycosis?
generally in tropical and subtropical areas on FEET exposed to infected soil? Agricultural workers and mine workers
How is the location of white piedra different from that of black piedra?
White piedra is facial, axillary, and pubic hair whereas black piedra is only on the face and scalp
What causes white piedra? Black piedra?
White piedra = trichosporon spp; black piedra = piedraia hortae
What is the difference in appearance between endothrix lesions and ectothrix lesions?
Endothrix = fungi inside hair shaft, hair breaks and does not leave black dots; Ectothrix = fungi outside of hair, hair breaks and leaves little black dots
Name the 3 major dermatophytes
Microsporum, trichophyton, and epidermophyton floccosum
What are the two main agents to cause mycetoma (starred organisms)?
Actinomyces and Nocardia
What is the difference between dermatophytoses and dermatomycoses?
Dermatophytoses are superficial cutaneous infections that only invade superficial layers; Dermatomycoses are similar but they go deeper than just the epidermis
What is a kerion?
an intense, painful, and boggy suppurative reaction often on the back of the neck and associated with cervical lymphadenopathy.
What disease may occur with Malassezia furfur in the presence of a catheter?
Catheter Associated Sepsis
What is the danger of tinea pedis? Why does the normal flora change?
Secondary infection from itching and–the normal flora changes because there are antibiotics produced by the fungus, this may also impact the secondary infection risk
How would you differentiate between erythrasma and tinea cruis?
erythrasma = corynebacterium minutissimum fluoresces coral red with Wood’s lamp, tinea cruis does not fluoresce
Which mycetoma granules are white?
Pseudallescheria boydii
What are the names for the asexual and sexual forms of pityriasis versicolor?
Asexual = Malassezia furfur; Sexual = Pityrosporum orbiculare
What is the most common zoophilic cause of tinea capitis worldwide?
Microsporum canis
What is a dermatophytid?
It is a secondary rash to the dermatophyte, it is caused by the immune system so there are no fungi present
Name the 4 superficial fungi (not the dermatophytes)?
Malassezia furfur (pityriasis versicolor); Horatea werneckii (tinea nigra); Trichosporon spp. (white piedra); Piedraia hortae (black piedra)
What is the most common mode of transmission for a systemic mycosis?
respiratory (i.e. coccidiodes etc.)
What immune response is needed to control Candidal infections?
T cell
What is contained in the granules of a Mycetoma?
microcolonies of the agent embedded
How do you get a mycetoma? What kind of inflammation?
Traumatic inoculation; granulomatous (subset of chronic)
How would you differentiate between tinea cruis and candida for jock itch?
Candida affects both the scrotum and thigh; Tinea cruis only affects the thigh? Yes I’m sure never in the history of the world has tinea cruis ventured to the scrotum
How do you grow Malassezia furfur? What is the likely significance of the fact that lesions occur in the distribution of sebaceous glands?
On solid media with olive oil since it requires long chain fatty acids to grow; sebum contains fatty acids!
How would you differentiate between the two causes of tinea capitis that fluoresce?
HISTORY, Microsporum canis is from an animal and Microsporum andouini is from a human
What is the most likely cause of tinea capitis in the U.S?
Trichophyton tonsurans
Which mycetoma granules are dark red to black?
M. mycetomatis
What is the name given to pigmented fungal cells in the pustules of a chromoblastomycosis?
Medlar body
What are some ways (4) that the hyphal form of Malassezia furfur can be induced?
Increased temperature, high humidity, greasy skin (teens), hyperhidrosis
What does it mean for a fungus to be dematiaceous?
The hyphae and/or spores are darkly pigmented because they contain melanin granules
