Question

1. What is the Theory of Spontaneous Generation? How did Louis Pasteur disprove this theory? What did his observations provide the basis for, and how has this impacted microbiology?
   

Answer 1

Theory of Spontaneous Generation:

This theory is said to have been given by Aristotle. The basis of the theory is obsolete. The theory suggests that living organisms can arise from non-living/ inanimate things.

For example,

• maggots from rotten meat,
• bread kept in a dark container produces mice, etc.

In 1688, This theory was first disproved by Francesco Redi when he took pieces of meat and placed them in different environments. One piece of meat under a piece of paper; one was placed under cheesecloth and one was left in the open air. The earlier belief was that maggots came spontaneously from rotten meat. But Redi was able to prove that only when flies were exposed to the surface of the meat, they laid eggs and that eventually became maggots. Like his belief, the piece of meat under paper or cheesecloth didn't give rise to maggots while the one exposed to air, gave rise to them supporting his theory.

Again came John Needham in 1745. He was using chicken broth to prove the Spontaneous generation theory. He believed that heating the broth would kill the microorganisms in it. After heating it for a while and let it cool down. There was appearance of turbid microbial growth and he suggested that life came spontaneously. His theory was disproved by Lazzaro Spallanzani. He did the same set of experiments but cut off the air source, and surprisingly no growth was observed.

In 1859, the entire confusion was put to an end by Louis Pasteur. Pasteur modified the experiment conducted by Spallanzani. He understood that the dust in the air contained microbial particles that gave rise to them in exposed sterile media. He took a heating flask, melted its neck, and carefully modifies it to a S-shaped curve, known as the swan flask. This was an ideal setup, that would allow the air to go into the sterile media but prevented the dust from entering. As a result, there was no microbial growth observed, but when he broke the neck of the flask and exposed the media to outside air and dust, he was able to observe microbial growth. Pasteur quoted: "Omne vivum ex vivo"- Life only comes from life.

This experiment of Pasteur formed the basis for the "germ theory of disease". This is because when he was trying to figure out why his wine was getting spoilt, he understood that using pasteurization one could kill the bacteria that cause spoilage but allow the yeast fermentation to alcohol. From this, he understood that diseases are caused by microorganisms. That's why he is rightly considered the "father of microbiology", having:

• Disapproved spontaneous generation theory
• Gave the germ theory of disease
• Found the causes of fermentation
• Gave the method of Pasteurization.
• Create vaccines for anthrax, fowl cholera, and rabies.

This period led to the Golden Age of Microbiology, where the findings of Pasteur enabled the development of antibiotics. Eventually, the development of Biotechnology also occurred. Modern microbiology was able to:

• Quality control in the dairy and food industry
• Use of microorganisms in industries for vitamins, enzymes, fermented products.
• Development of the pharmaceutical industry
• The killing of microorganisms in drinking waters
• Microorganisms as living factories.