Introduction to Microbiology

What is Microbiology?

• Study of microscopic organisms: bacteria, viruses, fungi, protozoa.
• Many microorganisms are beneficial:
  • Humans: Aid in digestion.
  • Plants: Bacteria responsible for nitrogen fixation.
  • Animals: Help in cellulose digestion.
• Industrial applications of microorganisms.

Classification of Microorganisms

• Bacteria: Categorize by Gram stain (positive or negative).
• Viruses: Categorize by genome (DNA/RNA, single/double-stranded).
• Fungi: Categorize into molds (multicellular) and yeasts (unicellular).

Hierarchy of Classification

• Mnemonic: Dina's kids prefer candy over fried green spinach.
• Levels: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Domains:
  1. Bacteria: Prokaryotes.
  2. Archaea: Prokaryotes.
  3. Eukarya: Eukaryotes.
• Kingdoms:
  • Bacteria: One kingdom - Bacteria.
  • Archaea: One kingdom - Archaea.
  • Eukarya: Four kingdoms - Protists, Fungi, Plants, Animals.

Prokaryotes vs Eukaryotes

• Prokaryotes: (Bacteria & Archaea)
  • No cytoplasmic structures (e.g., mitochondria, Golgi apparatus, ER).
• Eukaryotes: (Eukarya)
  • No cell wall except in fungi and plants.
  • Different ribosome structures.

Focus on Bacteria

• Naming Conventions: Two-part names (Genus species).
  • Example: Staphylococcus aureus
  • Genus: Staphylococcus
  • Species: aureus
• Shapes Descriptions:
  • Cocci: Round cells.
    • Staphylococcus: Clusters like grapes.
    • Diplococci: Pairs.
    • Streptococci: Chains.
    • Tetrads: Packets of four.
  • Bacilli: Rods.
  • Spiroschets: Curved.
  • Cocobacilli: Mix of rod and round.
  • Vibrious: Curved rod.

Bacterial Architecture

• General Structure: Genetic material, cell membrane, and cytoplasm.
• Additional Structures:
  • Cell wall: Protection and structure.
  • Flagella: Locomotion.
  • Pili: Attachment.
  • Plasmid: Extra-chromosomal genetic material.
  • Glycocalyx: Protective layer (capsule or biofilm).
  • Porins: Transmembrane proteins for molecule passage, can mediate antibiotic resistance.
  • Mesosomes: Equivalent to mitochondria in eukaryotes, used for respiration.

Gram Staining

• Purpose: Classify bacteria based on cell wall constituents and Gram stain reaction.
• Gram Positive:
  • React with Gram stain: Blue color.
  • Thick peptidoglycan layer with techoic and lipotechoic acids.
• Gram Negative:
  • React with Gram stain: Red/Pink color.
  • Structures:
    1. Plasma membrane.
    2. Thin peptidoglycan layer.
    3. Outer membrane with phospholipids, trans-systable proteins & lipoproteins.
    4. Lipopolysaccharide layer (O antigen, core polysaccharide, lipid A/endotoxin).
• Endotoxins: Present only in Gram-negative bacteria; antigenic, elicit immune responses (fever, weakness, aches, shock).

Conclusion

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