Bacterial Classification: Size, Shape, and Features

Bacterial Classification: Size, Shape, and Features

Bacterial Structure

  • General Features: Bacteria are single-celled organisms with specific shapes.
  • Diagrammatic Representation: The lecture refers to a diagram showcasing a generic bacteria, noting that not all bacteria possess every feature illustrated.
  • Organelles:
    • Ribosomes: Small organelles present in bacteria.
    • Cytoplasm: A gel-like fluid within the bacteria where ribosomes reside.
    • Fimbriae/Pili: Hair-like projections extending from the bacteria's surface.
    • DNA: Nuclear material located centrally or at one end, not enclosed by a membrane.
    • Plasmid: Separate DNA material.
    • Inclusion: Spheres within the bacteria containing various substances.
    • Flagella: Tails enabling movement through solutions.
    • Plasma Membrane: Membrane surrounding the cytoplasm.
    • Cell Wall: Located outside the plasma membrane.
    • Capsule: Outermost layer.

Bacterial Shapes

  • Bacillus: Rod-shaped bacteria.
  • Coccus: Spherical or round bacteria.
  • Spirillum: Spiral-shaped bacteria.
  • Cell Wall: Often composed of peptidoglycan.
  • Reproduction: Primarily through binary fission.
  • Motility: Some bacteria move using flagella.

Size Comparison

  • Visual Scale:
    • Visible to the human eye: Lice, bread mold reproductive structures.
    • Light Microscope: Amoeba, white blood cells, red blood cells, Rickettsia bacteria, E. Coli, Staphylococcus.
    • Electron Microscope: Viruses.
    • Special Microscopes: Molecules.
  • Size Range: Bacteria range from 0.50.5 to 22 micrometers in diameter.
  • Comparison: A blood cell is approximately 7.57.5 micrometers in diameter.
  • Micrometer Definition: One-thousandth of a millimeter.
  • Advantage of Small Size: Nutrients can easily enter through the cell membrane, reaching all parts of the bacteria.

Bacterial Shapes and Arrangements

  • Shapes:
    • Coccus: Round, spherically shaped.
    • Bacillus: Rod-shaped.
    • Coccobacillus: Intermediate between round and rod-shaped.
    • Spirillum: Spiral shape.
    • Spirochete: Longer, tighter spiral shape.
    • Vibrio: Curved shape.
  • Arrangements:
    • Streptococcus: Cocci arranged in a chain.
    • Staphylococcus: Cocci clustered together.
    • Diplococci: Two cocci together.
    • Sarcina: Cocci in a three-dimensional cube.
    • Tetrad: Cocci in a flat cube.

Flagella and Motility

  • Function: Long fibers that enable bacteria to move through solutions.
  • Swarming: Bacteria in a petri dish with agar and blood demonstrate swarming behavior.
    • Growth Pattern: Bacteria grow and multiply in periods, creating lines as they move towards areas with more nutrients.
    • Example: Proteus species.
  • Classification by Flagella:
    • Monotrichus: Single flagellum at one end.
    • Lophotrichus: Tuft of flagella at one end.
    • Amphotrichus: Flagella at both ends.
    • Peritrichus: Flagella all around the bacteria.
  • Flagella Mechanism:
    • Motor: Drives the flagella.
    • Hook: Angled hook that causes the flagella to spin like a propeller.

Pili and Fimbriae

  • Types of Fibers: Pili and fimbriae are fibers not used for propulsion.
  • Pili:
    • Characteristics: Longer, thicker.
    • Occurrence: Gram-negative bacteria only.
    • Quantity: Fewer per cell (3-5).
    • Genetic Origin: Formed by genes in plasmids.
    • Function: Attaching to other cells for DNA exchange (sexual reproduction).
  • Fimbriae:
    • Function: Attaching to surfaces.
    • Example: E. Coli.
  • Antibody Defense: Antibodies can attack fimbriae to prevent bacterial attachment.
  • Disease Contribution: Fimbriae enable bacteria to stick to mucous membranes, colonize, and reproduce.
  • Pellicle Formation: Bacteria stick together on the surface of water, forming a scum-like layer.
  • Distinction: Pili are thicker, tubular, and involved in genetic information exchange (conjugation).
  • Conjugation: Transfer of genetic material from one bacteria to another via sex pili.

Capsule

  • Composition: Polysaccharide called glycocalyx.
  • Location: Outside of the bacteria.
  • Functions:
    • Protects from drying out.
    • Enables sticking to surfaces.
  • Example: Streptococcus mutans forms layers on teeth, causing tooth decay.
  • Phagocytosis Prevention: The capsule prevents phagocytosis by blocking complement penetration.

Cytoplasm and Osmotic Shock

  • Cytoplasm:
    • Composition: 80% water, the rest is protein and salt.
    • Importance: Water content is crucial for survival.
  • Genetic Material:
    • DNA: Circular and single set (haploid).
    • Advantage: Efficient growth and prone to mutations for quick adaptation.
    • Plasmid: Extra part of DNA that can replicate independently and provide antibiotic resistance.
  • Organelles: Lack complex organelles, except for smaller ribosomes.
  • Osmotic Shock:
    • Cause: Sudden change in the concentration of solution around the cell.
    • Process: In a solution with no salt, water enters the saltier cell cytoplasm via osmosis.
    • Result: The cell expands, potentially rupturing due to the increased water intake.