Investigate the work of Robert Koch and Louis Pasteur

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Investigate the work of Robert Koch and Louis Pasteur, to explain the causes and transmission of infectious diseases, including:

  • Koch’s postulates
  • Pasteur’s experiments on microbial contamination

Louis Pasteur:

  • Discovered that infectious diseases are caused by micro-organisms. Known as his ‘Germ Theory of Disease’.
  • Experiment:
    • Sought to disprove the theory of spontaneous generation.
    • Hypothesized that microbes were in the air everywhere, and food spoils when these microbes land there and become active.
    • Poured nutrient broth into 2 identical swan-neck flasks, and boiled both of them to kill of all microbes.
    • Then he broke of the necks and left both flasks out in open air.
    • As he predicted, the flask with the broth open to the air developed cloudy bacterial growths, while the flask with the swan-neck stayed clear
    • This proved that the microbes that spoil food come from the air, and disproved spontaneous generation.
  • Pasteur and Fermentation:
    • Pasteur examined samples of fermenting wines under the microscope.
    • He observed yeasts, which were converting the sugars to alcohol.
    • He also observed bacteria, which were converting sugars to lactic acid.
    • The bacteria were also observed in sour milk and were the cause of food spoilage.
    • Pasteur showed that heating the wine or milk to 55ºC for a few minutes kills the microbes that spoil them. This process is called pasteurization.

Robert Koch:

  • Studied anthrax disease. Anthrax is a bacterial disease that affects sheep and humans.
  • Process of his investigation:
    • Obtained infected matter from a sheep suffering from anthrax
    • Placed it on a slide, observed it under a microscope and saw active rod-shaped
    • cells and inactive dormant spores.
    • Established that the blood of animals with disease always contained these micro-organisms, while the blood of healthy animals did not.
    • He found that if blood from an infected animal was injected into a healthy animal, it would cause disease.
    • He grew cultures of the rod-shaped bacteria to infect mice – they developed the disease. This proves that it was the bacteria, and not any other blood component that caused the disease.
  • Koch’s Postulates: (for establishing that a certain microbe causes a disease)
    • The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
    • The microorganism must be isolated from a diseased organism and grown in pure culture.
    • The cultured microorganism should cause disease when introduced into a healthy organism.
    • The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.