The History and Impact of Microbiology

Posted on Nov 8, 2024 in Biology

Microbiology

Concept of Microbiology

Microbiology is the science that studies microorganisms (MO), whose size is below the resolving power of the human eye (<100µ).

This definition implies that its object of study is determined by the methodology:

  • Microscopes
  • Laboratory techniques of pure culture
  • Etc.

History of Microbiology

Discovery of Microorganisms

Antonij van Leeuwenhoek
  • Developed a simple microscope
  • Discovered microorganisms (“animalcules” in pond water, 1674)
  • Described bacteria and protozoa
Robert Hooke
  • Made a compound microscope
  • Described filamentous fungi (1667) using a simple microscope similar to Leeuwenhoek’s

First pictures of bacteria (Leeuwenhoek)

Classification of Microorganisms

Before the discovery of microorganisms, it was believed that all living organisms were either plants or animals. Plants and animals could be easily distinguished, while knowledge of microorganisms was scarce.

To avoid arbitrary classifications, Ernest Haeckel in 1866 proposed the kingdom of Protista, including algae, fungi, protozoa, and bacteria.

The Great Nineteenth-Century Dispute Resolution

The Debate on Spontaneous Generation

  • Ideas taken from Aristotle
  • Redi (1668): Experiments ruled out the spontaneous generation of animals.
    • Omne vivum ex ovo
    • Omne ovum ex vivo
  • But spontaneous generation was still not universally accepted.
  • The Dispute Between Spallanzani and Needham
    • The experiments were misinterpreted (Needham), claiming that heating the jars caused the air to lose its “life force” (vitality).
  • Pasteur Settles the Controversy Over Spontaneous Generation
    • Experiments with open-air bottles equipped with long, curved necks (swan neck).
    • After boiling, no microorganisms appeared if the bottle remained upright.
    • Microorganisms appeared if the liquid reached the curved neck.
    • The curved neck acted as a trap to capture microorganisms.

The Debate on Ferments

  • Two theories about the origin of fermentation: chemical and biological
  • Pasteur (1857) was called to solve a problem in the Lille refineries in 1857: lactic acid fermentation caused by bacteria.
  • 1860: Alcoholic fermentation caused by yeast.
  • Discovery of butyric fermentation and life in the absence of air (anaerobic).
  • Reconciliation of the two theories: Buchner isolated a cell-free preparation (zymase) from yeast.

Technical Advances: Pure Culture

  • Two theories about how microorganisms exist: pleomorphism and monomorphism
  • The debate was resolved using pure cultures (laboratory of Robert Koch).
  • Solid media based on potato slices
  • Solid media based on gelatin
  • Solid media based on agar-agar
  • Petri (in Koch’s laboratory) invented the Petri dish.
  • Enrichment and differential media (Beijerink, Winogradsky)

Technical Advances: Microscopes and Staining Techniques

  • Koch worked with the German glass industry (Schott) and sought help from experts in optics (Abbe, Zeiss).
  • Improved achromatic lenses
  • Lower capacitor lighting
  • Immersion objective (1878)
  • Koch worked with the chemical industry BASF:
  • Developed stains to observe bacteria (methylene blue, fuchsin, gentian violet, etc.), 1877 onwards.
  • Ziehl-Neelsen: Differential staining for acid-fast bacteria (1883)
  • Hans C. Gram: Gram stain differential (1884)

Role of Microorganisms in Infectious Diseases

Speculative Period (Theological)

Microbial activities were known to humanity without any knowledge of microorganisms.

Speculative Period (Miasma)

Miasma, Lucretius, Fracastorius (1545) proposed the idea of “seed germs” of disease that live in food and fermented drinks (cheese, milk, wine, beer).

Pasteur’s Work on Infectious Diseases

  • Pasteur resolved a silkworm disease (pébrine). In 1869, he identified the protozoan Nosema bombycis.
  • Studied avian cholera
  • Worked on rabies

Koch’s Contributions

  • Koch (1876): Using his pure culture technique, he experimentally isolated and propagated for the first time a pathogenic bacterium responsible for anthrax.
  • First micrographs of Bacillus anthracis stained with methylene blue.
  • Confirmed that this bacterium presents a resistant phase (endospores).
  • The disease could be reproduced experimentally by re-inoculating bacilli into laboratory animals.

Koch’s Postulates (1882)

  1. The pathogen must be present in all cases of the disease.
  2. The pathogen must be isolated from the diseased host and grown in pure culture.
  3. The pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
  4. The pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen.

The School of Koch: Numerous Pathogens Isolated

  • Cholera (1883)
  • Diphtheria (1884)
  • Tetanus (1885)
  • Pneumonia (1886)
  • Meningitis (1887)
  • Plague (1894)
  • Syphilis (1905)

Asepsis and Chemotherapy

  • The introduction of anesthesia (mid-nineteenth century) led to surgical infections.
  • Lister introduced the use of phenol and mercury salts (aseptic surgery).
  • Paul Ehrlich: The idea of “magic bullets”
  • Collaborated with chemists and discovered Salvarsan (compound 606) against syphilis.
  • Chemotherapy