Micro: Mycoses Flashcards
What are the basics of pityriasis (tinea) versicolor?
young people at beginning of puberty, SUPERFICIAL
multiple macules - variable appearance, hypopigmented, surrounded by normal skin, midline and symmetrical
high temp and humidity favors occurrence
inf agent = *malassezia furfur = superficial mold
What is tinea nigra?
SUPERFICIAL fungal inf, appears as black spots
usually palms and soles
caused by hortaea werneckii
What is piedra?
nodules on outside of hair shafts, SUPERFICIAL ectothrix infections
black piedra from piedraia hortae
white piedra from trichosporon
How is pityriasis versicolor diagnosed?
clinical appearance, KOH prep
use Wood’s lamp - yellow to yellow-green fluorescence of scales from active lesions
skin samples have “spaghetti & meatballs” appearance
What are the therapeutic options for pityriasis versicolor?
topical agents and oral meds
What are the different ways to classify fungi?
mold vs. yeast: mold grow as hyphae, yeast as oval cells
monomorphic vs. dimorphic (yeast at 37 deg C, mold in environment)
imperfect (no sexual form) vs. perfect (sexual form)
What are basic features of the dermatophytes?
= cutaneous mycoses, invade stratum corneum only and other keratinized tissues (hair and nails)
lesions are serpentine or annular w raised margins
monomorphic - only mold, colorless spores
arthroconidia = infective form, also macro and micro
What are the 3 genera of dermatophytes?
microsporum: hair, skin
epidermophyton: skin, nail
trichophyton: hair, skin, nail
What are the basic clinical features of inf w dermatophytes?
skin: circular, dry, erythematous, itchy, scaly lesions
hair: scarring, alopecia
nails: thickened, disformed, discolored, subungual debris
Where do zoophilic vs. anthropophilic organisms usually affect?
z - exposed areas (face, neck, arms)
a - occluded areas, areas of trauma
What mold is suggested by spindle-shaped macroconidia?
microsporum canis, radial yellow appearance on plate
What mold is suggested by dumbbell-shaped macroconidia?
epidermophyton floccosum
What are ectothrix vs. endothrix invasions?
arthroconidia outside or inside the hair shaft
What are the modes of transmission for dermatophytes?
direct contact w lesions or contact w materials, animals, or soil
person to person, animal to human, or from environment
anthropophilic only humans, zoophilic mostly animals, geophilic in soil
Do dermatophytes disseminate? why or why not?
no - can’t grow at body temp (37 C)
How do dermatophytes invade keratinized tissues?
produce keratinases and proteinases
How are the dermatophytes diagnosed?
growin in Sabouraud’s dextrose agar = acidic pH 5.2 mimics skin
What do the following color colonies suggest:
greenish-brown or khaki
pale, yellowish-brown or reddish-brown from under plate
white from top of plate
E. floccosum
Trichophyton
Microsporum
What does trichophyton look like?
many spherical microconidia clustering on hyphae
few macroconidia
What is an id reaction?
to dermatophytes = a hypersensitivity rxn
rash and vesicles on skin distant from site of inf
What is the basic treatment of dermatophyte inf?
topical or systemic
oral agents concentrate in keratinocyts and also found in sweat
usually a couple of weeks
recurrences common after stopping therapy
What is the basic treatment of onychomycosis?
topical therapy ineffective
systemic therapy for several months
itraconazole and terginafine DOC but potentially hepatotoxic
What is sporotrichosis?
subcutaneous inf caused by sporothrix schenckii
dimorphic fungus
What is the histological appearance of sporotrichosis?
yeast = cigar shaped budding yeast
mold = thins septate hyphae w daisy-like conidia, darkly pigmented
demo may be difficult because fungi not abundant
What is the reservoir and modes of transmission of sporothrichosis?
soil, moss, hay, decaying wood, vegetation
risks = occupational (rose handler’s dz from thorn pricks)
usually direct inoculation, rarely inhalation in alcoholics and COPD
What are the dz manifestations of sporotrichosis?
minor trauma and inoculation through skin
subcutaneous lesions - chronic, firm, nonhealing nodules, sometimes ulcerate and ooze serous fluid
spreads along lymphatics - become firm and cordlike –> nodules in LINEAR arrangement, progresses proximally
no constitutional symptoms unless bacterial inf
When and how does sporotrichosis spread outside the subcutaneous layer?
osteoarthritis in immunocompetent
disseminated in immunocompromised –> osteoarticular and pulmonary, poor prognosis
rarely subacute pneumonia w inhalation - can look like Tb or histo in immunocompromised
What are the lesions of sporotrichosis made of?
suppurating granulomas - histiocytes and giant cells surrounded by neutrophils, lymphocytes and plasma cells
What is the general treatment for sporotrichosis?
saturated potassium iodide for most forms
itraconazole and terbinafine effective
amphoterecin B for disseminated
What is chromoblastomycosis?
chronic localized inf of skin and subcutaneous tissue
produces raised, warty, scaly lesions, usually on legs (“cauliflower like”)
What are the dz manifestations of chromoblastomycosis?
most follow minor traumatic inoculation
small papule at site of trauma - enlarges to form nodule w friable surface - then spread laterally for satellite lesions
lesions usually not painful, but can ulcerate and bleed
can encircle leg and cause lymphatic obstruction
overlying skin becomes hyperkeratotic and pigmented
lesions can be there for yrs, bacterial superinfection common
acute and chronic granulomatous inflammation, microabscesses, reactive fibrosis
What cause chromoblastomycoses?
dark walled pigmented fungi = dematiaceous fungi that produce melanin like pigment
*most common cause is Fonsecaea pedrosoi)
How are chromoblastomycoses diagnosed?
skin scrapings and punch biopsies
large clusters of fungal cells appearing brown
grow slowly over 4 wks
What is the general treatment for chromoblastomycoses?
itraconazole and terbinafine prolonged therapy (6 mos-1 yr)
What is mycetoma?
chronic progressive granulomatous inf of skin and subcutaneous tissue, can progress to bone
usually legs, most often foot
local swelling, draining sinus tracts, production of granules in tracts
How does mycetoma infect?
inoculation following minor trauma w thorns, splinters
PMNs cannot destroy –> granulomatous response
incubation 5-10 yrs
spread is rare
What is the microbiology of mycetoma?
actinomycotic and eumycotic types
a: caused by filamentous bacteria
e: caused by fungi, white grain or dark grain mycetoma
How is mycetoma diagnosed?
clinical hx, long duration of symptoms, painless soft tissue welling, sinus tracts and grains in drainage
culture can identify causative organism
What is the treatment for mycetoma?
amphoterecin B not effective for eumycetoma
oral useful, but cure is rare
long durations of therapy, often amputation
antibacterials for bacterial causes
