fungi

MYCOSES

• Definition: Illnesses caused by fungi.

• Can be superficial (skin, nails), subcutaneous, or systemic (lungs, bloodstream).

• Often opportunistic — occur when the immune system is weakened

THALLUS {Fungal Body}

• The thallus = main body of a multicellular fungus.

• Composed of filaments called hyphae.

• Many hyphae tangled together form a mycelium (like a network or mat).

• Two types of hyphae:

  • Septate hyphae: have cross-walls (septa) dividing the cells.

  • Coenocytic (non-septate) hyphae: no walls between cells → continuous cytoplasm with many nuclei.

HOW DO YEAST DIFFER FROM MOLDS

• Yeasts: Unicellular, reproduce by asexual budding, smooth colonies; Candida albicans

  • Molds: Multicellular, reproduce via spores, fuzzy colonies; Penicillium

DEFINE DIMORPHIC FUNGI

• Dimorphic = “two forms.”

• Can exist as:

  • Mold in the environment (cool temps, 25 °C)

  • Yeast in host tissues (body temp, 37 °C)

• Example: Coccidioides immitis (Valley Fever) — mold in soil, yeast in lungs

HOW ARE FUNGAL CELL WALL CHEMICALLY DIFFERENT FORM BACTERIAL CELL WALLS?

• Fungi: contain chitin (a polysaccharide with nitrogen).

• Bacteria: contain peptidoglycan.

• → This difference is important for drug targeting (antifungals vs. antibiotics).

HOW DO FUNGAL CELL MEMBRANES DIFFER FROM ANIMAL/HUMAN CELL MEMBRANES

• Fungal membranes: have ergosterol instead of cholesterol.

• Ergosterol is targeted by antifungal drugs like miconazole and amphotericin B.

HOW ARE FUNGAL SPORES DIFFERENT FROM BACTERIAL ENDOSPORES

FUNGAL SPORES= Reproduction, not highly resistant, EX: mold spores on bread

BACTERIAL ENDOSPORES= Survival, extremely resistant, bacillus

COCCIDIODES, VALLEY FEVER

• Found in dry soil (e.g., Arizona, California).

• Mold in soil; when spores are inhaled → convert to yeast in lungs.

• Causes respiratory illness, fever, chest pain, fatigue.

• Dimorphic fungus; infection risk rises after dust storms

WHY ARE EUKARYOTIC INFECTIONS DIFFICULT TO TREAT

• Because fungi are eukaryotic like humans — their cells share:

  • Ribosomes

  • Cytoskeleton

  • Membrane structure

• So antifungal drugs risk harming human cells.

• Only major difference = ergosterol and chitin, which serve as drug targets.

• Even so, antifungals have more toxic side effects than antibiotics