microbiology fungal

Cell Wall

• Made of chitin and β-glucans (especially β-1,3-glucans).

• Provides rigidity and protection.

• Humans do not have cell walls → good drug target.

Cell Membrane:

• Contains ergosterol (instead of cholesterol found in humans).

• Another selective target for antifungals.

Antifungal Mechanisms

Polyenes (Amphotericin B, Nystatin)

• Target: Ergosterol in the fungal cell membrane.

• Mechanism:

  • Bind ergosterol → form pores → ions leak → osmotic imbalance → cell death.

• Toxicity: Can also bind cholesterol (low affinity) → nephrotoxicity.

conazole

inhibit ianosterol 14-a-demethylase

cytochrome P-450-dependent enzyme

side effect: teratogenic birth defects

Echinocandins

target: β-1,3-glucan synthase in the fungal cell wall.

• Mechanism:

  • Inhibit synthesis of β-1,3-glucans → weakened wall → osmotic lysis.

• Note: Mammalian cells lack β-glucans → highly selective and safe.

mycotoxin

ingested, inhaled, or direct contact