USMLE Step 1-Mycology Question and Answer
Sabouraud's agar - Fungi Fungal spores - Most fungal spores are asexual. Both coccidioidomycosis and histoplasmosis are transmitted by inhalation of asexual spores. Conidia = asexual fungal spores (e.g., blastoconidia, athroconidia) Histoplasmosis - Dimorphic fungi that can cause systemic mycosis, endemic to Mississippi and Ohio river valleys. Causes pneumonia. In bird or bat droppings. Intracellular (tiny yeast inside macrophages [below]): img src="158a - Histoplasmosis.JPG" / Blastomycosis - Dimorphic fungi that can cause systemic mycosis, endemic to states east of Mississippi River and Central America Causes inflammatory lung dz and can disseminate to skin and bone. Forms granulomatous nodules. Big, Broad-Based Budding: img src="158b - Blastomycosis.JPG" / Culture on Sabouraud's agar. Coccidioidomycosis - Dimorphic fungi that can cause systemic mycosis, endemic to Southwestern USA, California. Causes pneumonia and meninngitis; can disseminate to bone and skin. Found in San Juaquin Vally or desert (desert bumps) vally fever img src="158c - Coccidioidomycosis.JPG" /img src="Coccidioidomycosis.JPG" / Paracoccidioidomycosis - Dimorphic fungi that can cause systemic mycosis, endemic to rural Latin America Captain's wheel appearance (budding yeast below): img src="158d - Paracoccidioidomycosis.JPG" / Dimorphic fungi - (Histoplasmosis, Blastomycosis, Coccidioidomycosis, and Paracoccidioidomycosis) Mold in soil (@ lower temps) and yeast in tissue (@higher/body temp: 37C), except coccidioidomycosis, which is a spherule in tissue. Cold = Mold, Heat = Yeast All can cause pneumonia and can disseminate. Tx: fluconazole or ketoconazole for local infxn, amphotericin B for systemic infxn. Systemic mycoses can mimic TB (granuloma formation) Geography of systemic mycoses/dimorphic fungi - img src="158e - Fungi geography.JPG" / Tinea versicolor img src="159a - Tinea versicolor.JPG" / - Caused by Malassezia furfur. Occurs in hot, humid weather. Tx: topical miconazole, selenium sulfide (Selsun). Spaghetti and meatballs appearance on KOH prep.
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