Introduction to Microbiology

Definition of Microbiology

• Study of microscopic organisms: bacteria, viruses, fungi, protozoa.
• Most microorganisms are beneficial:
  • Humans: Normal microbiota aids digestion.
  • Plants: Bacteria assist in nitrogen fixation.
  • Animals: Aid in cellulose digestion.
  • Industries: Various uses.

Classification of Microorganisms

Bacteria

• Gram Stain:
  • Positive or Negative.

Viruses

• Classified by genome type:
  • DNA or RNA.
  • Single-stranded or double-stranded.

Fungi

• Divided into:
  • Molds (multicellular).
  • Yeasts (unicellular).

Hierarchy of Classification

• Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.
• Mnemonic: Dina's kids prefer candy over fried green spinach.

Domains

• Bacteria, Archaea, Eukarya.
  • Prokaryotes: Bacteria, Archaea.
  • Eukaryotes: Eukarya.

Kingdoms

• Bacteria: One kingdom: Bacteria.
• Archaea: One kingdom: Archaea.
• Eukarya: Four kingdoms: Protists, Fungi, Plants, Animals.

Focus on Bacteria

Naming

• Two-part name: Genus + Species.
  • Example: Staphylococcus aureus (Staphylococcus = genus, aureus = species).
  • Names can indicate shape: "staphylo" (cluster), "coccus" (round).

Shapes of Bacteria

• Cocci: Round cells.
• Bacilli: Rods.
• Spirochetes: Curved.
• Diplococci: Two cocci.
• Cocco-bacilli: Mix of rod and round.
• Vibrios: Curved rod.
• Streptococci: Chains of cocci.
• Staphylococci: Irregular clusters.
• Tetrads: Cocci in packet of four.

Bacterial Architecture

• Genetic Material, Cell Membrane, Cytoplasm.
• Cell Wall, Flagella (locomotion).
• Pili (attachment).
• Plasmid: Extra genetic material.
• Glycocalyx: Protection (capsule or biofilm).
• Porins: Transmembrane proteins, mediate antibiotic resistance.
• Mesosomes: Equivalent to mitochondria, used in respiration.

Gram Staining

Classification by Gram Staining

• Gram Positive: Stains blue.
• Gram Negative: Stains red or pink.

Cell Membrane Differences

• Gram Positive:
  • Thick peptidoglycan layer.
  • Contains teichoic and lipoteichoic acids.
• Gram Negative:
  • Thin peptidoglycan layer.
  • Outer membrane with phospholipids.
  • Lipopolysaccharide layer (endotoxin).

Endotoxins

• Present in gram-negative bacteria.
• Cause immune response: fever, weakness, aches, shock.

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