Differentiating Bacteria: Shape and Color

Observing Bacteria Under Microscope

• Scientists/pathologists use microscopes to observe bacteria.
• Bacteria can be seen in different colors and shapes.

Identifying Bacteria by Colors

• Bacteria can appear in various colors (e.g., purple, pink).
• Vertically: top rows are purple; bottom rows are pink.

Identifying Bacteria by Shapes

• First row: Circular/Spherical shape (cocci/coccus).
• Second row: Rod-like shape (bacilli/bacillus).
• Third row: Squiggle shape (spirilla/spirochete).

Staining Bacteria: The Gram Stain

• Gram stain colors the external layers of bacteria.
• Purple: Gram-positive bacteria.
• Pink: Gram-negative bacteria.

Gram Stain Mechanism

• Gram-positive: Thick peptidoglycan wall retains purple stain.
• Gram-negative: Thin peptidoglycan wall, outer membrane, lipopolysaccharide layer (LPS), retains pink stain after washing.

Bacterial Cell Wall Structure

Gram-positive Bacteria

• Layers:
  • Inner plasma membrane.
  • Thick peptidoglycan layer (sugar chains connected by proteins).
  • Capsule (slime layer).

Gram-negative Bacteria

• Layers:
  • Inner plasma membrane.
  • Thin peptidoglycan layer.
  • Outer membrane.
  • Lipopolysaccharide (LPS) layer.
  • Capsule.
  • Periplasmic space: Between layers.

Summary

• Shapes: Cocci (spherical), Bacilli (rod-like), Spirilla (squiggle).
• Gram Stain: Differentiates bacteria based on cell wall structure.
• Gram-positive: Thick peptidoglycan, stains purple.
• Gram-negative: Thin peptidoglycan, LPS, stains pink.