Week 2 P2 Notes

Capture Resisting Phagocytosis

• Mechanism employed by white blood cells to attach to surfaces.
• Negative staining technique used to visualize capsules around bacteria, producing a halo effect.
• Example: Klebsiella pneumoniae shows a capsule in negative stain, resulting in a halo around the rod shape.

Ribosomes

• Site of protein synthesis in cells.
• Composed of two subunits: 50S and 30S (S = Svedberg units, a measure of sedimentation).
• Analogy: Compared to a MasterChef kitchen for cooking up proteins.

Nucleoid

• Contains the chromosomal DNA of the bacterial cell.
• Similar to a nucleus but not membrane-bound as in eukaryotes.
• Features double-stranded DNA; large genomes may require supercoiling to fit within the nucleoid.

Fimbriae and Flagella

• Fimbriae (Pili):

  • Hair-like appendages; slender tubes made of helically arranged proteins.
  • Function: Help bacteria stick to surfaces (e.g., within a host).
  • Capable of lengthening by adding new subunits.

• Flagella:

  • Long, whip-like structures observed under scanning electron microscopy (SEM).
  • Example: Proteus vulgaris has multiple flagella allowing for swarming motility on agar plates.
  • Motion facilitated by the helical structure of flagella spinning like a propeller.

Bacterial Flagella Distribution

• Monotrichous: One flagellum at one pole.
• Amphitrichous: One flagellum at each end.
• Lophotrichous: Cluster of flagella at one or both ends.
• Peritrichous: Flagella distributed all over the surface.

Bacterial Movement

• Flagella rotate at high speeds (up to 100,000 RPM).
• Differentiation from Brownian motion: true movement vs. mere random movement in liquid due to water molecule collision.
• Example: Pseudomonas fluorescens exhibits tumbling movement; swarming typically observed in Proteus vulgaris.

Endospores

• Produced by certain bacterial species, making them highly resistant to harsh conditions.
• Key processes:
  • Sporulation: Formation of endospores during adverse conditions (nutrient depletion).
  • Germination: Return to vegetative state when conditions are favorable.
• Resistant to heat, UV radiation, and chemical disinfectants.
• Important for food safety concerns, e.g., Clostridium botulinum.

Pathogenicity Concepts

• Pathogenicity: Ability of an organism to cause disease.
• Virulence: Degree of pathogenicity; intensity of disease caused.
• Virulence Factors: Characteristics contributing to an organism's ability to cause disease, such as toxins and adhesion molecules.

Exotoxins

• Soluble, heat-labile proteins secreted by pathogens.
• Example: Botulinum toxin (Clostridium botulinum) interferes with neurotransmitter function, causing paralysis.
• Heat inactivation can neutralize these toxins; essential for food safety measures.
• Common types:
  • A-B toxins: Two-subunit structure affecting host cells.
  • Superantigens: Cause excessive immune responses.

Examples of Pathogens and their Effects

• E. coli (various strains can cause UTIs, diarrhea, etc.)
  • Virulence factors facilitate adherence to host tissues.
• Staphylococcus aureus: Produces toxins that cause various human diseases, including toxic shock syndrome and skin peeling.
• Clostridium species: Participate in necrotizing infections and produce various types of toxins affecting cellular functions.

Application and Importance

• Understanding bacterial features and pathogenic mechanisms is crucial in microbiology, medicine, and disease prevention.
• Lab activities focus on identifying specific virulence factors and testing pathogens using techniques like coagulase testing and selective agar plates for isolating organisms.