Louis Pasteur: the bicentennial of a French national hero

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As France prepares to commemorate the bicentennial of his birth, Louis Pasteur is mostly remembered by the wider public for producing the first vaccine against rabies. Yet, as it turned out, his interest for infectious diseases came rather late in his career. Indeed, shortly after defending his theses in physics and chemistry in 1847, his research focused initially on crystallography, the experimental science aimed at studying the structure and properties of crystals, including tartaric acids that occur naturally in many fruits, most notably grapes. Sounds complicated? How about the process of vinification, that is the conversion of grape juice into wine through fermentation? Pasteur established that such a process involves the intervention of microscopic living beings.

At the time of this major breakthrough, Pasteur was dean of the faculty of sciences in Lille, an industrial city located in the north of France. The story goes that the father of one of his students, who owned a distillery and wished to understand why beet-based alcohol could end up tasting like vinegar, asked him to investigate the phenomenon. In 1858, he released a Study on fermentation, the founding document on microbiology. Following his tenure in Lille, Pasteur published studies on wine and beer, in which he advocated the use of some chemicals and mild heat to stop bacterial contamination, a process known as pasteurization.

By the late 1860s, Pasteur had established himself as a leading scientist. His political ties with Emperor Napoleon III, whom he admired, no doubt helped. In 1868, Pasteur received the Legion of Honor. Two years later, he was made senator, just in time to witness the collapse of the Second Empire.

In the 1870s, Pasteur focused on various diseases affecting French agriculture: anthrax, chicken cholera or swine erysipelas, infections caused by a bacterium. At the same time, he endeavored to establish that micro-organisms play a key part in the outbreak of diseases through contagion. The term microbe was born. To be fair, Pasteur merely confirmed the existence of living germs associated with the development of a number of diseases. Such theory had been floating around since the 16th century. But his work helped answer the following question: are the germs responsible for the disease, or, rather, can they be considered its consequence? In 1863, thanks to Pasteur’s early findings on fermentation, Casimir Davaine, a French physician, identified the effects of anthrax in sheep. Around the same time, British surgeon Joseph Lister promoted the idea that post-operative infections killing patients in hospitals were the direct result of the same process of contagion observed in germs. He then successfully introduced the notion of sterilizing surgical instruments as well as the simple gesture of washing one’s hands to avoid infections.

The Franco-Prussian war of 1870-1871 and the humiliating French defeat gave Pasteur’s career a new impetus, for a rival from across the Rhine, Robert Koch, had emerged. Patriotism on both sides of the border became a key element in the rivalry between the two scientists. In the end, Pasteur and Koch are regarded as the two main founders of modern bacteriology. But, while Koch focused on isolating new pathogens, for example those responsible for typhoid fever, diphtheria, and pneumonia, Pasteur worked on already identified agents with the purpose of minimizing their impact. In 1879, he inoculated healthy chicken with chicken cholera bacteria culture, only to realize that the chicken did not die and were protected against new infections. He concluded that “weakened microbes” acted like a vaccine, the notion of vaccination having been invented at the end of the 18th century by English Physician Edward Jenner. In early 1881, Pasteur successfully conducted an anthrax vaccination experiment on sheep. The modern concept of “vaccine” was born. However, so far, no such experiment had been attempted on humans.

Pasteur went on producing the first vaccine for rabies, initially testing it on some twenty dogs. Despite the risk, he proceeded with the first human trial. In 1885, he injected 9-year-old Joseph Meister,

who had been badly bitten by a rabid dog, with the vaccine, an artificially weakened microbe. Within a few weeks, the boy was saved. It was a triumph for Pasteur. The episode officialized the validity of Pasteur (and Koch)’s germ theory of diseases. Financial donations poured and Pasteur was able to preside over the creation of a financially independent institute dedicated solely to research and vaccination, the now internationally renowned Institut Pasteur…