200th anniversary of Pasteur’s birth: “He is the Christopher Columbus of the microbial world”

A pioneer in microbiology, he is also the discoverer of the vaccine against rabies and, in addition, the “father” of vaccination: science and modern medicine owe a lot to Louis Pasteur, born on December 27, 1822 in Dole. Its 200th anniversary is the occasion for many celebrations. And a spotlight on a rich heritage.

Professor emeritus at the Faculty of Medicine in Montpellier, Jean-Pierre Dedet was for twenty years head of laboratory and head of services at the Institut Pasteur.

You worked at the Pasteur Institute, you are very involved in the celebration of the 200th anniversary…

Last September I gave a conference in Arbois (Ed. note: commune of Jura, which houses Louis Pasteur’s house and his laboratory), on the occasion of a special conference organized by the French Society for the History of Medicine, dedicated to the promotion of the Pasteur institutes around the world. There are currently 33 of them, on the five continents, this network is now called the Pasteur Network. They mainly conduct research, especially in the field of infectious disease prevention. We remain in the field of action of Pasteur, who was the great discoverer of infectious diseases and how to protect against them through vaccination. The first institute was established during Pasteur’s lifetime in Saigon, in 1891. It still exists, it is now called the Pasteur Institute in Ho Chi Minh City.

Montpellier resident Jean-Pierre Dedet worked for twenty years at the Pasteur Institute.

What is to be said, in a synthetic way, about the essentials of Louis Pasteur?

I would call him a discoverer. He is the discoverer of a new world, a Christopher Columbus of the microscopic world. Of course, the Dutch scientist Leeuwenhoek in the 17th century before him talked about animal balls. But it was Pasteur who discovered this world of microbes, some of which are useful, especially for fermentations, when he showed that it was a microbial phenomenon, and then certain pathogens. To me, Pasteur is really the discoverer of a new, microscopic, microbial world.

He was able to do it because he had the tools or because he was a genius, the Messi or Mbappé of science at the time?

A lot of it had to do with his personality. Pasteur was not a doctor, he was a chemist who had discovered molecular asymmetry, the way X-rays were interrupted by crystals according to their orientation. He had an extraordinary journey because from there he discovered that there were crystals of organic matter and crystals of mineral matter. It gradually passed to the existence of microbes, microorganisms. He showed, at a time when we believed in the theory of spontaneous generation, inherited from Aristotle, that the living was not created from nothing, but from something that already existed.

“With Pasteur we went from Aristotle to the modern world”

Did we go with Pasteur from Aristotle to the modern world?

Yes, because he was a man who experimented. Before him, we had counted on. He was a remarkable experimenter. Before him there had been Semmelweis, who had said that puerperal fever was transmitted, he had not proved it. Pasteur did it precisely and carefully. It is true that time also played a role: microscopy had just been invented.

He is therefore both the fruit of his time and a genius capable of standing out from his time to invent something else…

Inventing something different and demonstrating it, that is its great strength. That was the beginning of the experiment.

What we never lost sight of?

Absolutely, and thankfully. Medicine today is based on evidence.

But we could see that all this was fragile with the beliefs and false information, biased studies that we could see re-emerging during the Covid crisis!

Absolutely. But Pasteur also had to fight all his life against his opponents. But when he made his first vaccination against anthrax in cattle and sheep, he made a life-size experiment: he took a herd of cows and sheep, he gave instructions to inoculate his vaccine, then a month later with a very strong dose of anthrax. All the vaccinated animals were alive, the others were dead.

But vaccination is an extremely complex phenomenon: there are many vaccines and many mechanisms in these vaccines. The Covid vaccine does not prevent getting sick, it is dampening or neutralizing.

Pasteur invented a method of vaccination.

He was the first to design a vaccination, not empirically, but experimentally: how we achieve a weakening of the microbe, how its inoculation protects us. Pasteur’s genius was to take advantage of empirical observations. The word vaccination is a tribute to a precursor, the vaccinia virus that Jenner used in 1796 against smallpox.

“He was very controversial, especially when he condemned the theory of spontaneous generation”

Was Pasteur challenged?

Yes, he was very controversial, especially when he condemned the theory of spontaneous generation, which caused great debates in the academies of science and medicine. It was believed that living matter arose spontaneously. In the 17th century, Van Helmont said that to make mice appear, you only needed to heat dirty laundry. These ideas had been abandoned for animals, but they were still valid in the microbial world. Pasteur demonstrated that there were microbes everywhere.

We heard a lot during the Covid crisis that France remained the land of Pasteur, is it true?

Pasteur is widely known, and we are not proud enough to be Pasteur’s country. I worked in Bolivia. Arriving in the Andean highlands, a big smile lit up people’s faces when we talked about France, it was the Marseillaise and Pasteur. There are connections beyond those we imagine with modern medicine: it was on microbes cultivated by Pasteur that we discovered that DNA was the support of heredity. Modern molecular biology starts from microbiology, from the discovery of the microbial universe. Pasteur’s legacy is also food hygiene, the domestication of microbes for the food industry…

Finally, the Pasteur Institute is ten Nobel Prize winners. There is a French tradition that has remained very strong in research in microbiology and infection science. Although research today is no longer the work of a single man, it has become a collaborative phenomenon.

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