Prokaryotes vs. Eukaryotes

Prokaryotes vs. Eukaryotes

• Prokaryotes:

  • Genetic material not enclosed within a membrane, typically circular
  • Smaller size (1-4 µm)
  • Mostly unicellular
  • No true nucleus, nucleoid region
  • Simple cell wall
  • Cell division by budding or binary fission
  • No meiosis, DNA transfer only
  • Lack cytoskeleton and mesosomes
  • 70S ribosomes located in cytoplasm
  • Lack membrane-bound organelles
  • Lack extrachromosomal plasmids
  • Short cell cycle (20-60 minutes)

• Eukaryotes:

  • Genetic material enclosed within a membrane, linear
  • Larger size (greater than 5 µm)
  • Mostly multicellular
  • True nucleus enclosed by a membrane
  • Complex cell wall
  • Cell division by mitosis
  • Meiosis and sexual reproduction
  • Present cytoskeleton and mesosomes
  • 80S ribosomes located in cytoplasm or organelles
  • Present membrane-bound organelles
  • Present extrachromosomal plasmids
  • Longer cell cycle (12-24 hours)

Gram Stain

• Differentiates Gram-positive and Gram-negative bacteria.
• Gram-positive bacteria stain purple.
• Gram-negative bacteria stain red or pink.
• General rule: Most cocci are Gram-positive, except Neisseria, Veillonella, and Branhamella. Most bacilli are Gram-negative, except Corynebacterium, Clostridium, Bacillus, and Mycobacterium

Acid-Fast Stain

• Used for bacteria with high lipid content in their cell walls which cannot be stained using Gram stain.
• Two methods:
  • Ziehl-Neelsen (Hot Method): Requires steaming after primary dye application
  • Kinyoun (Cold Method): Does not require heat, oil-based primary stain.
• Acid-fast organisms stain red on a blue or green background.

Special Stains

• Used to demonstrate specific bacterial cell structures.
• Examples:
  • LAMB Stain (Loeffler Alkaline Methylene Blue): Stains metachromatic granules, capsule, or slime layer
  • Hiss Stain: Stains capsules or slime layers
  • Dyer Stain: Stains cell walls
  • Fischer-Conn Stain: Stains flagella
  • Dorner and Schaeffer-Fulton Stains: Stains spores
  • India Ink/Nigrosine: Stains capsules of Cryptococcus neoformans

Differential Stains

• Differentiate one group of bacteria from another.
• Two common types: Gram stain and acid-fast stain.