Microbiology and Disease Concepts

Microorganisms Overview

• Microbes Definitions:
  • Bacteria: Non-compartmentalized cells.
  • Archaea: Similar to bacteria but exhibit some eukaryotic traits.
  • Viruses: Composed of protein and nucleic acid; require a host for replication.
  • Eukaryotes: Compartmentalized cells containing organelles (e.g., nucleus).
  • Fungi: Eukaryotic organisms that can have filamentous cellular forms.

Domains of Life

• Three domains:
  • Prokaryotes: Comprised of Bacteria and Archaea.
  • Archaea:
  • Lack peptidoglycan in cell walls.
  • Have a protective protein surface known as the 'S-layer'.
  • 16s rRNA: Acts as a molecular clock to decipher evolutionary relationships.

Taxonomy and Identification

• The importance of taxonomy and identification in recognizing organisms.

The Scientific Method

• Characteristics:
  • Unbiased: Important in avoiding misinterpretation, but validity must be established.
  • Rigorous: Structured and controlled to ensure repeatability.
  • Falsifiable Hypothesis: Must be testable and capable of being proven wrong.
  • Reproducible: Results should be verifiable by various researchers.
  • Cumulative: Builds upon the foundational work of other scientists.
• Learning: According to Jean Piaget, children learn through hypotheses and repeated testing.

Case Study: Barry Marshall

• In an experimental approach, he ingested Helicobacter pylori, leading to gastritis that supported his theory of ulcers caused by this bacterium.
• H. pylori Characteristics:
  • Curved, Gram-negative bacterium.
  • Infects the stomach, resulting in gastric mucosa inflammation.
  • Produces urease, which neutralizes stomach acid, contributing to infection and potential ulceration.

History of Microbiology

Contributions of Early Scientists

• Microscopy Evolution:
  • 1595: Hans Jansen invents the microscope.
  • 1665: Robert Hooke publishes Micrographia, discovers cells.
  • 1674: Antonie van Leeuwenhoek describes "animalcules" (microorganisms).

Cell Theory

• Proposed by Robert Hooke:
  • All living things comprised of cells.
  • All cells arise from pre-existing cells.

Four Key Questions in Microbiology

1. Spontaneous Generation:

   • Concept that living organisms can arise from non-living matter.
   • Early observations proposed by Aristotle and later expanded by researchers (e.g., John Needham).

2. Role of Fermentation:

   • Investigated by Louis Pasteur to understand spoilage, particularly in wine, leading to the development of pasteurization.
   • Identified yeast and bacteria during fermentation processes.

3. Understanding Diseases:

   • Historical beliefs about causes (bad vapors, evil spirits).
   • Progression through empirical research (e.g., Sushruta Samhita, Agostino Bassi).

Germ Theory and Koch's Postulates

• Robert Koch's Contributions:
  • Germ theory explains infectious diseases.
  • Developed Koch's Postulates to establish a causative relationship between pathogens and diseases:
  1. The pathogen must be found in diseased individuals and absent in healthy ones.
  2. Pathogen must be isolated and grown in pure culture.
  3. The cultured pathogen should cause the disease when introduced into a healthy host.
  4. The same pathogen must be re-isolated from the newly diseased host.

Innovations in Medicine

• Infection Control:
  • Ignaz Semmelweis advocated handwashing in hospitals to reduce childbed fever mortality.
  • Joseph Lister introduced aseptic techniques in surgery, leading to a significant decrease in surgical deaths.

Cholera Epidemic and Disease Mechanisms

• John Snow's Epidemiology Studies:
  • Identified Vibrio cholerae as the agent causing cholera from contaminated water (Broad Street pump).
• Cholera Characteristics:
  • Signs/Symptoms: 'Rice water' diarrhea, dehydration, low white blood cells in stool.
  • Virulence Factor: Cholera toxin disrupts ion flow, causing electrolyte imbalance and severe dehydration.
• Transmission: Through fecally contaminated water or undercooked seafood.
  • Treatment involves rehydration therapy (oral or IV) and possible antibiotic use (doxycycline).

Conclusion

• Knowledge gained from historical figures paved the way for modern microbiology and continuous research in pathogen behavior, disease control, and preventive medicine.