Mycology

Candidiasis

Key Virulence:

• Dimorphic fungus; forms pseudohyphae and budding yeast at lower temperatures, true hyphae (germ tubes) at body temperature.
• Part of normal flora; opportunistic in immunocompromised.
• Germ tubes indicate invasive form.

Buzzwords / Clinical:

• Cutaneous, mucocutaneous, or systemic infections.
• Oral thrush, vaginal discharge, diaper rash, satellite skin lesions, esophagitis (AIDS-defining).
• Seen in obesity, diabetes, infants, and patients on antibiotics/steroids.

Diagnosis:

• KOH prep shows budding yeast with pseudohyphae.
• Germ tube test for invasive strains.

Treatment:

• Topical: Clotrimazole, miconazole, nystatin (binds ergosterol → membrane pores).
• Systemic: Fluconazole (inhibits ergosterol synthesis).
• Invasive: Caspofungin (blocks β(1,3)-D-glucan synthesis), Amphotericin B (binds ergosterol, forms pores).

Aspergillosis

Key Virulence:

• Monomorphic mold with septate hyphae and acute angle branching (45°).
• Catalase-positive.
• Forms spores that are inhaled.

Buzzwords / Clinical:

• Invasive lung disease, fungus balls (aspergilloma), ABPA (asthma, CF).
• Immunocompromised: pleuritic pain, hemoptysis, halo sign or Monod sign on imaging.

Diagnosis:

• Biopsy with silver stain: septate hyphae, acute angles.
• Galactomannan antigen test.

Treatment:

• Invasive: Voriconazole or posaconazole (inhibit ergosterol synthesis).
• ABPA: corticosteroids.
• Prophylaxis in neutropenic patients: posaconazole.

Sporotrichosis (Sporothrix schenckii)

Key Virulence:

• Dimorphic fungus; cigar-shaped yeast in tissue, mold in culture (daisy clusters).
• Traumatic inoculation (e.g. rose thorn).

Buzzwords / Clinical:

• Rose gardener’s disease.
• Subcutaneous nodules spreading along lymphatics (ascending lymphangitis).

Diagnosis:

• Tissue biopsy shows cigar-shaped yeast.
• Culture shows daisy cluster mold.

Treatment:

• Itraconazole (inhibits ergosterol synthesis).
• Severe: Amphotericin B (binds ergosterol, forms membrane pores).

Blastomycosis

Key Virulence:

• Dimorphic fungus: mold in environment, yeast in tissue.
• Broad-based budding yeast.
• Thick wall resists phagocytosis.

Buzzwords / Clinical:

• Mississippi and Ohio River valleys.
• Affects lungs, skin (verrucous lesions), bones (osteolytic lesions).
• Immunocompromised: disseminated disease.

Diagnosis:

• Broad-based budding yeast on silver or PAS stain.

Treatment:

• Mild/moderate: Itraconazole (inhibits ergosterol synthesis).
• Severe: Amphotericin B (binds ergosterol, forms pores).

Coccidioidomycosis

Key Virulence:

• Dimorphic fungus; forms spherules with endospores in tissue.
• Inhaled arthroconidia from desert soil.

Buzzwords / Clinical:

• Southwestern U.S. (e.g., Arizona, California).
• Valley fever: flu-like illness, erythema nodosum, arthralgia.
• Severe in immunocompromised: meningitis, pulmonary cavities.

Diagnosis:

• Spherules with endospores on histology.
• Culture and serology.

Treatment:

• Mild: Fluconazole or itraconazole (inhibits ergosterol synthesis).
• Severe: Amphotericin B (binds ergosterol, forms pores