ch5: eukaryotic microbes (protozoa & fungi)

Cell Wall of Fungi vs. Bacteria

• Fungal cell walls contain chitin.

• Bacterial cell walls contain peptidoglycan.

• Plant cell walls (for comparison) contain cellulose.

Why don’t antibiotics work against fungi?

• Antibiotics are designed to target bacterial features like peptidoglycan cell walls or bacterial ribosomes.

• Fungi don’t have those features, but instead:

  • Chitin cell walls

  • Ergosterol in their membranes (humans have cholesterol).

• This means antibiotics are ineffective against fungal infections.

• Special antifungal drugs are needed that target ergosterol or other fungal-specific features.

How Fungal Cells Differ from Human Cells

• Both are eukaryotic (have nucleus, organelles)

• But fungi have:

  • Cell wall with chitin (humans have no cell wall).

  • Ergosterol in membranes (humans have cholesterol).

• Growth: fungi prefer moist, slightly acidic conditions and can grow with or without light

Naegleria fowleri (AMOEBOZOA)

“Brain-eating” amoeba; causes rare amoebic encephalitis

Acanthamoeba (AMOEBOZOA)

pathogenic species cause amoebic keratitis (eye infection)

Entamoeba histolytica (AMOEBOZOA)

parasitic amoeba, causes amoebic dysentery

Plasmodium (APICOMPLEXANS)

causes malaria; complex lifecycle that involves a mosquito host

Toxoplasma gondii (APICOMPLEXANS)

causes toxoplasmosis; transmitted via car feces and undercooked meat

• birth defects, problematic for pregnant women

Giardia

• parasitic protozoa; forms a resting stage (cyst)

• GI infections/diarrhea

• transmitted through feces contaminating water supplies

basic features of fungi

• multicellular fungi - molds

  • made of hyphae (filaments)

    • with cell walls = septate hyphae

    • no cell walls between cells = coenocytic hyphae

  • mycelium (tangled hyphae)

  • thallus (body of flushy fungi)

• unicellular fungi

  • yeasts

  • budding yeasts (asexual process)

    • short chains of buds stuck together = pseudohypha

• dimorphic fungi

  • can appear as yeast or molds

  • change in appearance is often a response to fluctuations in environment (temp)

Which four groups of fungi contain human pathogens?

• zygomycota

• ascomycota

• basidiomycota

• microsporidia