Microbiology Fundamentals - Eukaryotes, Fungi, Protozoa, and Helminths

The History of Eukaryotes

• First eukaryotic cells appeared 2-3 billion years ago.

• Evolved from the last common ancestor with bacteria, archaea, and eukarya.

• Primitive eukaryotes were single-celled and independent.

• Cells aggregated over time, forming colonies and becoming specialized.

Eukaryotic Cell Structures

• Flagella: Thicker and structurally more complex than bacterial flagella, covered by an extension of the cell membrane.

• Cilia: Similar to flagella but smaller and more numerous, found in protozoa and animal cells.

• Glycocalyx: Outermost layer composed of polysaccharides, important for protection, adherence, and signal reception.

• Cell Wall: Rigid structure in fungi, composed of chitin or cellulose (different from prokaryotic cell walls).

• Cytoplasmic Membrane: Contains sterols for stability, serves as a selectively permeable barrier.

• Nucleus: Contains:

  • Nuclear envelope with pores for macromolecule migration.

  • Nucleolus: Site of RNA synthesis.

  • Chromatin: Made of DNA and histone proteins.

• Lysosomes: Contain enzymes for intracellular digestion and removal of cell debris.

• Vacuoles: Membrane-bound sacs for storing or digesting fluids and solid particles.

• Ribosomes: Eukaryotic ribosomes are 80S (60S + 40S subunits).

Fungi

• Macroscopic fungi include mushrooms and puffballs; microscopic fungi include molds and yeasts.

• Forms: unicellular, colonial, or complex/multicellular.

• Yeast: Round to oval shape, asexual reproduction through budding.

• Hyphae: Long, threadlike cells in filamentous fungi. Pseudohyphae are chains of yeast cells.

• Some fungi are dimorphic, taking either form depending on growth conditions.

• Nearly 300 species can cause human disease (community-acquired, environmental, or hospital-associated infections).

• Can cause allergies and produce lethal toxins.

• Play roles in:

  • Decomposing organic matter.

  • Forming associations with plant roots.

  • Producing antibiotics, alcohol, and vitamins.

• Heterotrophic, saprobic, or parasitic nutrition.

• Reproduce through hyphal growth and spores.

Protozoa

• Single-celled organisms, mostly harmless and free-living.

• Heterotrophic, requiring organic food sources.

• Trophozoite: motile feeding stage.

• Cyst: dormant, resistant stage.

Helminths

• Include tapeworms, flukes, and roundworms.

• Flatworms (Platyhelminthes): cestodes (tapeworms) and trematodes (flukes).

• Roundworms (Aschelminthes): cylindrical, unsegmented bodies.

• Complete life cycle: fertilized egg, larval, and adult stages.

• Nematodes: sexes are separate.

• Trematodes and Cestodes: hermaphroditic.

• Infection through:

  • Contaminated food, soil, water, or infected animals.

  • Oral intake or skin penetration.

• Adults mate in the definitive host; larvae develop in the intermediate host.

• Pinworm (Enterobius vermicularis): common intestinal infestation with a simple life cycle involving egg ingestion and perianal deposition.