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Overview of the Course

• Course Title: MCB 201 - General Microbiology

• Main Topics:

  • Morphology and structure of bacteria

  • Growth and reproduction of bacteria

  • Measurement of microbial growth

Morphology of Bacteria

• Definition: Morphology refers to the shape and structural features of bacterial cells, which contribute to their classification and pathogenicity.

• Size: Bacteria typically range from 0.5 to 10 micrometers in diameter.

• Characteristics:

  • Lack a nucleus and membrane-bound organelles (e.g., mitochondria, Golgi apparatus).

  • DNA is found in the cytoplasm (nucleoid) and not in chromatin form as in eukaryotic cells.

  • Structural components include mesosomes, ribosomes, cytoplasmic membrane, and peptidoglycan cell walls.

Bacterial Cell Structure

• Cell Wall: Composed of peptidoglycan (murein), providing rigidity and shape, and varying across different species.

• Cytoplasmic Membrane: Semi-permeable barrier involved in transport and housing various enzymes for cellular processes.

• Cytoplasm: Contains ribosomes and DNA, with areas rich in macromolecules.

• Plasmids: Small, circular DNA molecules that can replicate independently and facilitate genetic exchange.

• Nucleoid: The area in the cell where bacterial DNA is located; lacks a nuclear membrane.

• Spores and Cysts: Certain bacteria can form spores (endospores and exospores) that allow survival in extreme conditions.

Classification of Bacteria

• Based on Shape:

  • Cocci: Spherical; can be further distinguished into:

    • Diplococci: Cocci in pairs (e.g., Neisseria spp.)

    • Streptococci: Cocci in chains (e.g., Streptococcus pneumoniae)

    • Staphylococci: Cocci in irregular clusters (e.g., Staphylococcus aureus)

    • Tetracocci: Cocci in groups of four (e.g., Micrococcus spp.)

    • Sarcinae: Regular clusters (e.g., Sarcina ventriculi)

  • Bacilli: Rod-shaped; can be:

    • Diplobacilli: Rods in pairs

    • Streptobacilli: Rods in chains (e.g., Streptobacillus felis)

  • Spirilla: Helical, rigid bacteria (e.g., Helicobacter pylori)

  • Spirochetes: Flexible coiled organisms (e.g., Treponema pallidum)

External Structures of Bacteria

• Flagella:

  • Function: Movement; composed of protein and varies in arrangement.

  • Types:

    • Monotrichous: Single flagellum at one end (e.g., Vibrio cholerae)

    • Lophotrichous: Cluster of flagella at one end

    • Amphitrichous: One flagellum at each pole

    • Peritrichous: Flagella spread over the entire surface

    • Atrichous: No flagella

• Pili (Fimbriae):

  • Function: Aid in adhesion, bacterial conjugation, and forming infections.

• Capsules:

  • Composition: Usually polysaccharides, providing protection against phagocytosis and retaining moisture.

Bacterial Cell Wall Composition

• Peptidoglycan:

  • Composed of repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), linked by peptides.

  • Differences between types: Gram-positive bacteria have a thick peptidoglycan layer and stain purple, while Gram-negative bacteria have a thinner layer and an outer membrane containing lipopolysaccharides (LPS).

Functions of Bacterial Components

• Movement: Flagella enable motility and are key for swarming behaviors.

• Attachment: Capsules and pili allow bacteria to adhere to surfaces, increasing their virulence.

• Protection: The cell wall protects from osmotic pressure and mechanical damage.

Summary of Key Concepts

• The morphology and structure of bacteria significantly influence their functions, classification, and pathogenicity.

• Understanding the structure, classification, and functions of bacteria helps in microbiological studies and medical diagnosis.