USMLE Mycology

cherryberryliu's version from 2015-10-22 18:41

Microbiology: Mycology

Systemic Mycoses


Question Answer
all causepneumonia (can disseminate)
cold meansmold
heat meansyeast
Rx for local inffluconazole or ketoconazole
Rx for systemic infamphotericin
systemic mycoses mimicTB (granuloma formation)


DiseaseEndemic location and pathological features
histoplasmosisMississippi, Ohio river valleys, causes pneumonia; hides in macrophages, bird or bat droppings
blastomycosiseast of Mississippi R and central America, causes inflammatory lung disease, disseminates to skin and bone, forms granulomatous nodules, broad-base budding
coccidioidomycosisSW USA, California, pneumonia and meningitis, can disseminate to bone and skin, case rate incrs after earthquakes (spherules in dust thrown up in air), desert valley fever
paracoccidioidomycosisLatin America, "captain's wheel" formation

Cutaneous Mycoses

Question Answer
tinea versicolorcaused by Malassezia furfur, degrades lipids and produces damage acids that damage melanocytes and cause hypopigmented/hyperpigmented patches, occurs in humid weather, "spaghetti and meatball" appearance on KOH prep
tinea versicolor Rxtopical miconazole, selenium sulfide (Selsun)
tinea pedis (foot)/tinea cruris (groin)/tinea corporis (ringworm on body)/tinea capitis (head, scalp)pruritic lesions with central clearing like a ring, caused by dermatophytes (Microsporum, Trichophyton, Epidermophyton), mold hyphae in KOH prep not dimorphic, pets reservoir for Microsporum
Microsporum Rxtopical azoles

Opportunistic Fungal Infections

Question Answer
Candida albicanssystemic or supf, dimorphic (yeast with pseudohyphae in culture at 20C, germ tube formation at 37C--diagnostic), oral and esoph thrush in immunocompr (diabetes, AIDS, neonates, steroids), vulvovaginitis (diabetes, antibiotics use), diaper rash, endocarditis in IV drug users, disseminated candidiasis (to any organ), chronic mucocutaneous candidiasis
Candid albicans Rxnystatin for supf inf, amphotericin B for systemic inf
Aspergillus fumigatusallergic bronchopulmonary aspergillosis, lung cavity aspergilloma ("fungus ball"), invasive aspergillosis (esp immunocompr and those with chronic granulomatous disease), mold with septate hyphae that branch at acute angles, not dimorphic
Cryptococcus neoformanscryptococcal meningitis, cryptococcosis, culture on Sabouraud's agar, heavily encapsulated yeast, not dimorphic, found in soil and pigeon droppings, stains with India ink, latex agglut test detects polysacc capsular antigen, "soap bubble" lesions in brain
Mucor and Rhizopus sppmucormycosis, mold with irreg nonseptate hyphae branching at wide angles, mostly in ketoacidotic diabetic and leukemic patients. fungi prolif in blood vessel walls when there is excess ketone and glucose, penetrate cribiform plate, and enter brain. rhinocerebral, frontal lobe abscesses. headache, facial pain, black necrotic eschar on face cranial nerve involvement


Question Answer
Pneumocystitis jirovecicauses diffuse interstitial pneumonia. yeast, inhaled. usually asymp. immunosup predisposes. diffuse, bilateral CXR appearance. diag by lung biopsy or lavage. ID by methenamine silver stain of lung
Pneumocystitis jiroveci RxTMP-SMX, pentamidine, dapsone; start prophylaxis when CD4 drops <200 cells/mL in HIV
Sporothrix schenckiisporotrichosis. dimorphic fungus, lives on vegetation. traumatically introduced into skin ("rose gardener's" disease), causes local pustule or ulcer with nodules along draining lymphatics (asc lymphangitis). little systemic illness.
Sporothrix schenckii Rxitraconazole or potassium iodide


Question Answer
Histoplasmamacrophage filled with Histoplasma (smaller than RBC)
blastomycosisbroad-base budding (same size as RBC)
coccidioidomycosisspherule filled with endospores (much larger than RBC)
paracoccidioidomycosisbudding yeast with captain's wheel formation (much larger than RBC)
Malassezia furfur"spaghetti and meatball" appearance on KOH prep
Microsporummold hyphae on KOH prep, not dimorphic
Trichophytonmold hyphae on KOH prep, not dimorphic
Epidermophytonmold hyphae on KOH prep, not dimorphic
Candidapseudohyphae and budding yeasts at 20C, germ tubes at 37C
Aspergillus45 degree angle branching septate hyphae, rare budding fruit bodies
Cryptococcus5-10 um yeasts with wide capsular halo, narrow-based unequal budding
Mucorirreg board (empty-looking) nonseptate hyphae, wide-angle branching
Pneumocystissaucer-shaped yeast forms
Sporothrixcigar-shaped yeast forms, unequal budding

Treatment Summary

Question Answer
Histoplasmafluconazole or ketoconazole for supf inf, amphotericin B for systemic inf
blastomycosisfluconazole or ketoconazole for supf inf, amphotericin B for systemic inf
coccidioidomycosisfluconazole or ketoconazole for supf inf, amphotericin B for systemic inf
paracoccidioidomycosisfluconazole or ketoconazole for supf inf, amphotericin B for systemic inf
Malassezia furfurtopical miconazole, selenium sulfide (Selsun)
Candidanystatin for supf inf, amphotericin B for systemic inf
PneumocystisTMP-SMX, pentamidine, dapsone
Sporothrixitraconazole or potassium iodide