USMLE Step 1 Flash Cards

Dimorphic Fungi Blastomyces

Histoplasma

Coccidioides

Sporothrix

Body Heat Changes Shape for the dimorphic fungi

Pseudohyphae (Candida albicans)

• Hyphae with constrictions at each septum

Spore types

Conidia

Asexual spores; formed off hyphae; common; air-borne

Blastoconidia

“Buds” on yeasts (asexual budding daughter yeast cells)

Arthroconidia

Asexual spores formed by a “joint”

Spherules and Endospores (Coccidioides)

Spores inside the spherules in tissues

Malassezia furfur

Normal skin flora (lipophilic yeast)

Patient with blotchy hypo-pigmentation of skin

KOH scrapping shows “spaghetti and meatballs” or

“bacon and eggs” yeast clusters & short curved septate

hyphae

Treatment :

Topical selenium sulfide; recurs

Dermatophytes (group of fungi) Filamentous (monomorphic) fungi

Three genera:

Trichophyton – skin, hair and nails

Mircrosporum – hair and skin

Epidermophyton – skin and nails

Patient with scaly, ringlike lesions (Tineas) of skin. May involve hair shaft or

nails.

KOH scrapping shows athroconidia and hyphae

Treatment :

Topical imidazole or tolnafate

ID reaction (dermatophytID) = allergic response to circulating fungal antigens.

Sporothrix schenckii

Subcutaneous mycoses

Patient with subcutaneous/lymphocutaneous

mycetoma

Gardener, florist, basket weaver, or alcoholic rose-

garden sleeper disease (homeless)

Cigar-shaped yeast in pus

Treatment : intraconazole or amphotericin B

Histoplasma capsulatum

Deep fungal infection; dimorphic fungi

Normal patient with acute pulmonary; IC patient with chronic

pulmonary or disseminated infection (FUNGUS FLU)

States following drainages of Great Lakes to Gulf of Mexico

Exposure to bird or bat excrement

Sputum or blood cultures with mononuclear cells packed with

yeast cells (tiny yeast inside macrophages)

Treatment : Ketoconazole, amphotericin B

Coccidioides immitis Deep fungal infection; dimorphic fungi

Normal patient with erythema nodosum or self-resolving

pneumonia

IC patient with calcifying chronic pulmonary or disseminated

infections

Pregnant female in 3rd trimester, disseminated infection

Desert southwest

Sputum has spherules with endospores

Treatment : Amphotericin B

Blastomyces dermatitidis Deep fungal infection; dimorphic fungi

Normal patient with acute pulmonary symptoms

IC patient with chronic pulmonary or disseminated infection

North and South Carolina (otherwise coexists with

Histoplasma)

Sputum has broad-based, budding yeasts with double,

refractile cell walls.

Treatment : Amphotericin B

Aspergillus fumigatus Monomorphic filamentous OPPORTUNISTIC fungi

Patient with asthma allergies – growing mucous plugs in

lung

Patient with cavitary lung lesions – fungus ball

Patient with burns – cellulitis, invasion

IC patient – pneumonia, meningitis

Septate hyphae branch at acute angles

Treatment : Itraconazole or Amphotericin B

Candida albicans OPPORTUNISTIC fungi

Forms germ tubes at 37˚C; pseudohyphae & true hyphae when invades

tissues

Germ tube test demonstrates pseudohyphae and hyphae

IC patient, overuse of antibiotics – thrush, spread down GIT,

septicemia

IV drug abusers - endocarditis

Treatment :

topical or oral imidazoles; nystatin

Disseminated : Amphotericin B or fluconazole

Cryptococcus neoformans

Encapsulated (monomorphic) yeast;

OPPORTUNISTIC fungi

Pigeon breeder with acute pulmonary symptoms

Hodgkins/AIDS patient with meningitis

India Ink mount of CSF with encapsulated yeasts

Treatment : Amphotericin B + flucytosine until

afebrile (minumum 10 wks), then fluconazole

Mucor, Rhizopus, Absidia Ketoacidotic diabetic or leukemic patient with

rhinocerebral infection

Biopsy with non-septate irregular-width hyphae

branching at 90˚ angles.

Treatment :

High fatality rate (rapid growth and invasion)

Debride necrotic tissue & start Amphotericin B fast.

Pneumocystis jiroveci Obligate extracellular parasite

Premature infant or AIDS patient with atypical pneumonia

Biopsy with honeycomb exudates and silver-staining cysts

X-ray ground glass

Treatment :

TMP-SMX for mild

Dapsone for moderate to severe