The scientific discoveries of Louis Pasteur in the 19th century revolutionized medicine and continue to save the lives of millions of people today

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Rodney E. Rohde, Texas State University

(THE CONVERSATION) Some of the greatest scientific discoveries have not resulted in Nobel Prizes.

Louis Pasteur, who lived from 1822 to 1895, is arguably the most famous microbiologist in the world. He is widely credited with the germ theory of disease and for inventing the process of pasteurization – which bears his name – to preserve food. Remarkably, he also developed the vaccines against rabies and anthrax and made a major contribution to the fight against cholera.

But as he died in 1895, six years before the awarding of the first Nobel Prize, this prize does not appear on his CV. If he had lived in the era of Nobel Prizes, he would undoubtedly have earned one for his work. Nobel Prizes, awarded in various fields including physiology and medicine, are not awarded posthumously.

During today’s time of continued threats from emerging or re-emerging infectious diseases, from COVID-19 and poliomyelitis to monkeypox and rabies, it is impressive to look back on Pasteur’s legacy. His efforts fundamentally changed the way people think about infectious diseases and how to fight them with vaccines.

I have worked in public health and medical laboratories specializing in viruses and other microbes, while training future medical laboratory scientists. My career began in virology, at the forefront of detecting and monitoring rabies and zoonotic agents, and it is largely based on Pasteur’s pioneering work in microbiology, immunology and vaccinology.

First a chemist

In my opinion, Pasteur’s most important contributions to science are his remarkable achievements in the field of medical microbiology and immunology. However, its history begins with chemistry.

Pasteur studied under the French chemist Jean-Baptiste-André Dumas. During this time, Pasteur became interested in the origins of life and worked in the field of polarized light and crystallography.

In 1848, just months after earning his doctorate, Pasteur was studying the properties of crystals formed during winemaking when he discovered that the crystals were in a mirror image, a property known as chirality. This discovery became the foundation of a sub-discipline of chemistry known as stereochemistry, which is the study of the spatial arrangement of atoms in molecules. This chirality, or laterality, of molecules was a “breakthrough hypothesis” at the time.

These discoveries led Pasteur to suspect what would later be proven by molecular biology: all life processes ultimately arise from the precise arrangement of atoms within biological molecules.

Wine and beer – from fermentation to germ theory

Beer and wine were essential to the economy of France and Italy in the 1800s. It was not uncommon during Pasteur’s lifetime for the products to spoil and become bitter or unsafe to drink. At the time, the scientific notion of “spontaneous generation” held that life can arise from non-living matter, which was believed to be responsible for the spoilage of wine.

While many scientists were trying to disprove the theory of spontaneous generation, in 1745 English biologist John Turberville Needham believed he had created the perfect experiment promoting spontaneous generation. Most scientists thought heat killed life, so Needham created an experiment to show that microorganisms could grow on food, even after boiling. After boiling the chicken broth, he placed it in a flask, heated it, then sealed it and waited, not realizing that air could get back into the flask before sealing it. After a while, the microorganisms grew and Needham was victorious.

However, his experiment had two major flaws. On the one hand, the boiling time was not enough to kill all the microbes. Most importantly, its vials allowed air to flow back, allowing for microbial contamination.

To settle the scientific battle, the French Academy of Sciences sponsored a competition for the best experiment to prove or disprove spontaneous generation. Pasteur’s response to the competition was a series of experiments, including an award-winning essay in 1861.

Pasteur considered one of these experiments “unassailable and decisive” because, unlike Needham, after having sterilized his cultures, he preserved them from contamination. Using his now famous gooseneck flasks, which had a long S-shaped neck, he let air in while preventing falling particles from reaching the broth during heating. As a result, the vial remained free of growth for an extended period. This showed that if air was not allowed directly into his boiled infusions, then no “living microorganisms would appear, even after months of observation”. However, and above all, if dust was introduced, living microbes appeared.

Through this process, Pasteur not only disproved the spontaneous generation theory, but also demonstrated that microorganisms were everywhere. When he showed that food and wine spoiled due to contamination by invisible bacteria rather than spontaneous generation, the modern germ theory of disease was born.

The origins of vaccination in the 1800s

In the 1860s, when the silk industry was devastated by two diseases that infected silkworms, Pasteur devised a clever process to examine silkworm eggs under a microscope and save those that were healthy. Much like his endeavors with wine, he was able to apply his observations to industry methods and he became something of a French hero.

Even with failing health following a severe stroke that left him partially paralyzed, Pasteur continued his work. In 1878, he succeeded in identifying and cultivating the bacteria responsible for the avian disease avian cholera. He recognized that the old bacterial cultures were no longer harmful and that chickens vaccinated with old cultures could survive exposure to wild strains of the bacteria. And his observation that surviving chickens were shedding harmful bacteria helped establish an important concept now all too familiar in the age of COVID-19 – asymptomatic “healthy carriers” can still spread germs during outbreaks.

After bird cholera, Pasteur turned to the prevention of anthrax, a widespread plague of livestock and other animals caused by the bacterium Bacillus anthracis. Drawing on his own work and that of German physician Robert Koch, Pasteur developed the concept of attenuated or weakened versions of microbes for use in vaccines.

In the late 1880s he showed beyond doubt that exposure of cattle to a weakened form of anthrax vaccine could lead to what is now well known as immunity, greatly reducing the mortality of the cattle.

The breakthrough rabies vaccine

In my professional assessment of Louis Pasteur, the discovery of the rabies vaccination is the most important of all his accomplishments.

Rabies has been called “the world’s most diabolical virus”, spreading from animal to animal through a bite.

Working with the rabies virus is incredibly dangerous, as mortality approaches 100% once symptoms appear and without vaccination. Through astute observation, Pasteur discovered that drying out the spinal cord of dead rabid rabbits and monkeys resulted in a weakened form of the rabies virus. By using this weakened version as a vaccine to gradually expose dogs to the rabies virus, Pasteur showed that he could effectively immunize dogs against rabies.

Then, in July 1885, Joseph Meister, a 9-year-old French boy, was badly bitten by a rabid dog. With Joseph facing almost certain death, his mother took him to Paris to see Pasteur because she had heard that he was working to develop a cure for rabies.

Pasteur took charge of the case and, alongside two doctors, he gave the boy a series of injections over several weeks. Joseph survived and Pasteur shocked the world with a cure for a universally fatal disease. This discovery opened the door to the widespread use of Pasteur’s rabies vaccine around 1885, which dramatically reduced rabies deaths in humans and animals.

A life worthy of a Nobel Prize

Pasteur once said in a famous lecture: “In the fields of observation, chance favors only the prepared mind”.

Pasteur had a knack for applying his brilliant—and prepared—scientific mind to the most practical dilemmas facing mankind.

While Louis Pasteur died before the Nobel Prize was opened, I would say that his incredible life of discoveries and contribution to science in the fields of medicine, infectious diseases, vaccination, medical microbiology and immunology places him among the greatest scientists of all time.

This article is republished from The Conversation under a Creative Commons license. Read the original article here: https://theconversation.com/louis-pasteurs-scientific-discoveries-in-the-19th-century-revolutionized-medicine-and-continue-to-save-the-lives-of-millions – today-191395.

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