Contribution of Louis Pasteur in Microbiology.

Who Was Louis Pasteur?

Louis Pasteur was a French chemist and microbiologist who is regarded as one of the founder of modern bacteriology and microbiology. He was born in 1822 at Dole in France. His work is considered as the foundation of microbiology and immunology.

In the early period of his career, he studied chemistry, physics and crystallography. It was during this time that molecular chirality was discovered by him in 1847. This discovery is referred to as stereochemistry. It showed that molecules having same chemical composition can differ in spatial arrangement.

Later, his interest was shifted towards biological and industrial problems. It was demonstrated by him that fermentation is a biological process caused by living microorganisms such as yeast and not a simple chemical decomposition. This work led to the rejection of spontaneous generation theory. In his swan-neck flask experiment, it was proved that microorganisms does not arise from non-living matter but are introduced from air and dust.

To prevent spoilage of wine, beer and milk, a heating process was developed by him. This process is known as pasteurization. It is the process of heating liquids at a definite temperature to kill harmful bacteria without destroying its main qualities. This method is still used in preservation of milk and other beverages.

Among the important contribution of Louis Pasteur is the germ theory of disease. It was stated that specific microorganisms are the cause of specific infectious diseases in humans and animals. This theory changed the concept of disease and helped in development of antiseptic surgical practices, thereby reducing surgical mortality.

In the later stage of his life, he worked on immunology. Vaccines were developed by him using weakened forms of pathogens. These are called attenuated vaccines. Vaccines for chicken cholera and anthrax was prepared successfully. In 1885, the rabies vaccine was administered to a nine-year-old boy, which gave him international fame.

To continue his research work, the Pasteur Institute was established in Paris in 1888. His discoveries have saved many lives and his contribution in the field of science is still remembered.

Contribution of Louis Pasteur

Louis Pasteur was a French scientist who gave major contribution in microbiology and medical science. His works are important in fermentation, germ theory, and vaccine development. Some of the main contribution are–

1. Molecular Asymmetry and Stereochemistry

• In 1848, molecular chirality was discovered by him.
• Left-handed and right-handed crystals of tartaric acid were separated under microscope.
• It was established that asymmetry is a distinct feature of organic world.
• This is referred to as foundation of stereochemistry.

2. Microbial Fermentation

• It was proved that fermentation is a biological process driven by living microorganisms (yeast).
• It was shown that fermentation is not a spontaneous chemical decomposition.
• Anaerobic life was also discovered.
• It was demonstrated that certain organisms can survive without oxygen.

3. Pasteurization

• A process was invented to prevent spoilage of liquids like wine beer and milk.
• In this process, the liquid is heated for short time between 55°C and 100°C (131°F to 212°F).
• Harmful bacteria and molds are killed without altering basic quality of the liquid.
• This process is referred to as pasteurization.

4. Refuting Spontaneous Generation

• Spontaneous generation theory was disproved by swan-neck flask experiment.
• It was demonstrated that microorganisms do not appear spontaneously from non-living matter.
• Microorganisms are introduced by airborne dust and germs.
• This experiment provided conclusive evidence against spontaneous generation.

5. Germ Theory of Disease and Medical Hygiene

• Foundational proof was provided that microscopic organisms are the cause of infectious diseases.
• This concept is referred to as germ theory of disease.
• It laid the groundwork of modern hygiene.
• Surgeons like Joseph Lister were inspired to follow antiseptic practices (sterilizing instruments and hand-washing) to prevent postoperative infections.

6. Saving the Silk Industry

• Two distinct silkworm diseases were identified (pébrine and flacherie).
• A microscopic cellular selection method was developed to screen infected female moths.
• Only healthy eggs were used for breeding.
• This work rescued French and European silk industries.

7. Birth of Immunology and Attenuated Vaccines

• The method of artificially weakening (attenuating) pathogens in laboratory was pioneered to create immunity.
• The term “vaccine” was coined in honor of Edward Jenner’s work with cowpox.
• Some vaccine developments are–
  • Chicken Cholera – First laboratory-attenuated vaccine was developed by aging the bacteria (virulence was reduced).
  • Anthrax – A highly successful vaccine was developed for sheep and cattle, and efficacy was proved in 1881 public trial at Pouilly-le-Fort.
  • Swine Erysipelas – A vaccine was co-developed to protect pigs with assistant Louis Thuillier.
  • Rabies – A post-exposure vaccine was prepared using dried spinal cords of infected rabbits and it was administered to human in 1885 saving a boy named Joseph Meister.

The Swan Necked Flask experiment of  Louis Pasteur

Louis Pasteur designed the swan necked flask experiment to disprove spontaneous generation. It was demonstrated that microorganisms does not arise from air by itself but they comes from pre-existing germs carried with dust.

1. Objective

• The main objective was to challenge the doctrine of spontaneous generation.
• It was believed that living microorganisms could arise spontaneously from air or from non-living matter.
• Pasteur wanted to prove that this belief is wrong.

2. Apparatus

• Special glass flasks were used in this experiment.
• These flasks had very long thin and curved S-shaped necks (swan neck).
• The neck was kept open to allow entry of air.

3. Preparation

• The flask was partially filled with nutrient rich broth (infusion).
• Filtered grape must was used as an example of infusion.
• The broth was boiled to kill any pre-existing germs (sterilization).
• This heating method later became known as pasteurization.

4. Mechanism

• The curved neck was the important part in this experiment.
• It allowed oxygen and atmospheric air to pass inside freely.
• It also prevented unwanted microbes from reaching the broth.
• Airborne dust particles carrying germs and fungal spores were trapped in the wet walls of the S-shaped bend.
• Due to gravity the dust settled down and remained in the bend and did not reach the sterile broth.

5. Primary Observation

• When the flask was kept undisturbed, the broth remained clear and sterile.
• No microbial growth was seen even after long time.
• It was demonstrated that pure air alone is not capable of producing microbial growth.

6. Crucial Test

• To prove the dust as the source, the curved neck was broken off in some flasks.
• In some cases the flask was tilted so that broth washed the contaminated walls of the bend.
• The sterile broth was allowed to come in contact with trapped dust.

7. Result of Contamination

• After exposure to dust, microorganisms appeared in the broth.
• They multiplied rapidly and the liquid was spoiled.
• This showed that the dust carried the living germs.

8. Conclusion

• It was concluded that microorganisms do not spontaneously generate from nothing.
• They arise from pre-existing microbes present on dust particles in environment.
• This experiment disproved spontaneous generation and it also supported germ theory of disease.

How the swan-neck flask experiment disproved spontaneous generation

The swan-neck flask experiment was designed by Louis Pasteur to disprove spontaneous generation. It was demonstrated that microorganisms does not arise from non-living matter or from pure air. They are introduced by pre-existing microbes carried on airborne dust particles.

1. Preparation and Sterilization

• A glass flask with a long thin S-shaped curved neck was taken (swan neck).
• The body of flask was partially filled with nutrient rich broth (infusion).
• The broth was boiled strongly.
• By this heating, the germs already present in the liquid were killed and the broth was made sterile.

2. Trapping mechanism of the curved neck

• The curved neck was kept open so that oxygen and atmospheric air can enter freely.
• But the S-shaped bend acted as a barrier for microbes.
• As air entered, dust particles carrying germs and fungal spores settled down due to gravity.
• These dust particles were trapped in the curve and they could not reach the sterile broth.

3. Primary observation

• When the flask was kept upright and undisturbed the broth remained clear and sterile for long time.
• No microorganisms were produced in the broth.
• It was proved that pure air alone cannot trigger generation of life in the broth.

4. Definitive proof by exposing broth to dust

• To confirm dust as the real source, the curved neck was broken off or the flask was tilted.
• By tilting, the sterile broth washed against the contaminated walls of the neck.
• Once the broth came in contact with trapped dust, microorganisms appeared.
• They multiplied rapidly and spoiled the broth.

5. Conclusion

• It was concluded that microorganisms does not originate spontaneously from nothing.
• They comes only from pre-existing life present on dust particles.
• This experiment gave strong evidence against spontaneous generation and it supported germ theory of disease.

How Louis Pasteur’s work revolutionize the brewing and wine industries

Louis Pasteur changed the brewing and wine industries by proving that fermentation is a biological process. It is driven by living microorganisms (mainly yeast). Before his work it was believed that fermentation is only a chemical decomposition and spoilage was considered unavoidable.

Key ways in which the industries were transformed are–

1. Fermentation was explained as a microbial process

• In 1856, he started investigation when M. Bigot asked help for beetroot alcohol which was souring.
• By microscope observation it was identified that good vats contained healthy budding yeast cells producing alcohol.
• The sour vats were found contaminated with rod-like bacteria producing lactic acid.
• It was demonstrated that spoilage occurs due to contamination and not due to spontaneous changes in liquid.

2. Pasteurization was introduced to prevent spoilage

• In 1863, he investigated why French wines were turning sour during export to Great Britain (requested by Napoleon III).
• The “diseases” of wine was proved to be caused by specific microbial contaminants.
• A method was developed where wine or beer is heated for short period between 55°C to 100°C (131°F to 212°F).
• Harmful bacteria and molds were killed without altering the main quality or bouquet of beverage.
• Shelf life of wine and beer was extended for months and long-distance transport became possible without spoilage.

3. Controlled brewing environment was emphasized

• After 1870 (Franco-Prussian War) he focused on helping French brewers to compete with German rivals.
• In 1876, he published Études sur la Bière (Studies on Beer) explaining that spoilage organisms enters through airborne dust or contaminated yeast.
• It was suggested that beer should be manufactured in more controlled condition with minimal air contact.
• A closed fermentation tank was designed so that airborne bacteria cannot enter into the brew.

4. Pure yeast strains and monitoring was promoted

• Microscopes and laboratory checking was introduced in breweries to monitor fermentation and contaminants.
• Brewers realized that suitable ferments can be isolated and cultivated (example Saccharomyces cerevisiae).
• Use of uncontaminated yeast strains made fermentation faster and more stable.
• The taste profile became more predictable and controlled because the same yeast can be reused without mixed contamination.

QNA on Contribution of Louis Pasteur

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