1. Fungal Structure & Antifungals
- Cell Membrane: Contains Ergosterol (Human = Cholesterol).
- Cell Wall: Contains Chitin, Glucans ($\beta$-1,3-glucan), Mannan.
| Drug Class | Target | Mechanism |
|---|
| Polyenes (Amphotericin B, Nystatin) | Membrane | Bind Ergosterol → Form Pores |
| Azoles | Membrane Synthesis | Inhibit 14-$\alpha$-demethylase |
| Allylamines (Terbinafine) | Membrane Synthesis | Inhibit Squalene Epoxidase (Early step) |
| Echinocandins (Caspofungin) | Cell Wall | Inhibit $\beta$-glucan synthesis |
| Griseofulvin | Microtubules | Inhibits mitosis (deposits in keratin) |
2. Morphology & Growth
- Yeast: Unicellular, reproduce by budding. (e.g., Cryptococcus).
- Mold: Multicellular hyphae.
- Septate: Walls present (Aspergillus).
- Aseptate/Coenocytic: No walls (Mucor, Rhizopus).
- Dimorphic: "Mold in the Cold (25°C), Yeast in the Beast (37°C)".
Exception: Coccidioides forms a Spherule in tissue.
3. Cutaneous Mycoses
- Dermatophytes: Secrete Keratinase. Infect Stratum Corneum.
Diagnosis: KOH Prep (Branching septate hyphae).
Tinea corporis (Body), cruris (Groin), pedis (Feet), unguium (Nails).
- Tinea Versicolor: Malassezia furfur. "Spaghetti & Meatballs" appearance. Lipid-dependent. Inhibits melanin.
- Sporotrichosis: Sporothrix schenckii. "Rose Gardener's Disease".
Cigar-shaped yeast. Ascending lymphangitis.
Tx: Itraconazole or Potassium Iodide.
4. Systemic Mycoses (Dimorphic)
All transmitted via Inhalation. Not person-to-person.
| Organism | Region | Morphology in Tissue |
|---|
| Histoplasma | Ohio/Miss. Valley | Macrophage filled with small yeasts (Small < RBC) |
| Blastomyces | East/Central US | Broad-based budding (Same size as RBC) |
| Coccidioides | Southwest US | Spherule w/ endospores (Large > RBC) |
| Paracoccidioides | Latin America | Captain's Wheel (Huge >> RBC) |
5. Opportunistic Mycoses
- Candida: Pseudohyphae & Yeasts. Germ Tubes at 37°C.
Diseases: Thrush (scrape-able), Esophagitis (AIDS), Vulvovaginitis (Diabetes/Abx).
- Aspergillus: Septate, Acute Angle (45°) branching.
Diseases: ABPA (Asthma/CF), Aspergilloma (Fungus ball in TB cavity), Invasive.
- Mucor/Rhizopus: Aseptate, Right Angle (90°) branching.
Risk: DKA (Diabetic Ketoacidosis).
Clinical: Black eschar on face, penetrates cribriform plate.
- Cryptococcus: Encapsulated yeast (Not dimorphic).
Stains: India Ink (Halo), Mucicarmine (Red capsule).
Clinical: Meningitis in AIDS.
- Pneumocystis (PCP): Disc-shaped yeast. Silver stain.
Clinical: Ground-glass pneumonia.
6. General Morphology (Text-Based Review)
- Fungal Cell Wall: Chitin, Glucans, Mannans.
- Fungal Cell Membrane: Ergosterol (Unique component; analogous to Cholesterol).
- Monomorphic: Exclusively Yeast OR Mold.
- Dimorphic: Exists as Mold or Yeast depending on temperature.
- Temperatures: Mold @ 20°C, Yeast @ 37°C.
- Examples: Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Sporothrix.
- Clinical: Commonly cause subacute pulmonary infections.
7. Advanced Morphology (Microscopic Details)
| Organism | Key Visual Feature | Distinction / "Look-alike" |
|---|
| Mucor | Ribbon-like, irregular width hyphae | Vs. Aspergillus (Uniform width) |
| Blastomyces | Thick, double-contoured wall | Broad-based budding |
| Cryptococcus | Narrow-based budding | Vs. Blastomyces (Broad-based) |
| Pneumocystis | "Crushed Ping-Pong Balls" | Cysts on Silver Stain |
| Sporothrix | Asteroid Body | Yeast w/ radiating eosinophilic material |
| Leishmania | Kinetoplast (Dark rod) | Vs. Histoplasma (No rod, cell wall halo) |
| Dermatophytes | Arthroconidia (Spores in hair) | Vs. Blastoconidia |