Pasteur and Koch


Pasteur’s contribution to microbiology is enormous. His greatest achievement was disproving the theory of spontaneous generation through his swan neck flask experiment. Pasteur observed John Needham and Lazzaro Spallanzani’s experiments where they boiled hay and Needham left the broth open to air while Spallanzani left the broth in air tight container. Needham observed microbes regrew in the medium despite him killing them all by boiling, whereas, Needham noticed no microbes returned. Pasteur developed his swan neck flask experiment to understand the discrepencies between the two experiments.

Pasteur put hay, which was a known source of microbes, into two swan neck flasks. He then boiled both flasks killing all the microbes which were on the hay making them sterile environments. From here Pasteur snapped the neck of one flask whilst leaving the other alone, this opened one flask up to the air. After leaving the flasks for a week, Pasteur noticed microbial growth within the flask open to the air, whilst no growth emerged from the flask closed to the environment.

Pasteur concluded there was no life force within inanimate objects, life can’t emerge from non-life, rather there are microbes within the air which cause microbial growth. This idea was revolutionary hence disproving spontaneous generation and proposing the germ theory of disease – a theory we still use today.

The process of pasteurization was developed from this theory, which is used to prevent milk and wine spoilage. Through heating these liquids to 60 degrees Celsius for a couple minutes, the microbes within them can be killed preventing spoilage saving multiple millions of dollars each year. Additionally, Pasteur pioneered fermentation and developed vaccines for rabbis.

Koch provided microbiology with multiple techniques such as staining to allow for different organelles within microbes to be seen under a light microscope. As well as using a solid growth medium to grow microbes. He also demonstrated Turberculosis and cholera were caused by bacterium’s. As well as Anthrax being caused by bacterium Bacillus anthracis which can remain dormant within the soil with spores.

However, Koch’s most notable contribution was Koch’s postulates. These allow scientists to determine whether microbes are the cause of disease. The steps used to link a microbes to a disease include:

  1. Extract the same microbe from all organisms infected with the disease and grow it in pure culture.
  2. Inoculate healthy susceptible hosts with the pure cultured microbe and monitor for disease after this.
  3. If the host develops the same symptoms as those from which the microbe is from, take a sample of the microbe.
  4. Regrow this microbe on pure culture and compare it to the original pure cultured microbe. If they are the same then this microbe is likely causing the disease.


Swan neck flask

Koch’s postulates


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