Timeline: Louis Pasteur, 1822–1895

Louis Pasteur was a French biologist and chemist who invented pasteurization, advanced the germ theory of disease, and developed vaccines for anthrax and rabies.

Pasteur made his early discoveries while working with the beer industry. He determined that yeast was the microorganism responsible for producing alcohol, and that bacterial contamination caused beer to sour. He also observed that alcoholic fermentation needed to occur under anaerobic conditions, a phenomenon that was named the Pasteur Effect. In 1862, Pasteur showed that briefly heating wine and milk prevented spoiling caused by bacterial growth. The process was called pasteurization and quickly gained widespread use.

The germ theory of disease, which states that many diseases are caused by microorganisms, is a cornerstone of modern medicine and clinical microbiology. The idea had been proposed by earlier thinkers, but Louis Pasteur and Robert Koch were the first to provide the proof that made germ theory a widely accepted fact. After filling flasks with sterile nutrient broth, Pasteur found that microbial growth occurred in flasks that were open to the air, but not in sealed flasks or swan-necked flasks that admitted air but not dust. These experiments proved that microbial growth came from invisible spores in the environment, and not from spontaneous generation in the broth itself.

In 1865, the French government commissioned Pasteur to investigate pébrine disease, which was killing silkworms and devastating the national silk industry. After three years, Pasteur discovered that pébrine was caused by a microorganism, and showed that disease could be prevented if healthy worms and eggs were separated from sick worms and contaminated materials. More importantly, evidence that microorganisms caused disease in animals further advanced germ theory. Pasteur's work led Edinburgh surgeon Joseph Lister to develop antiseptic procedures for surgery, which drastically reduced the number of deaths caused by infection.

Pasteur was also the first person to create vaccines artificially. In 1876, Koch had demonstrated that anthrax was caused by the bacterium Bacillus anthracis. Using heat to weaken the bacteria, Pasteur produced an attenuated anthrax culture that could be used as a vaccine. In 1881, he publicly inoculated sheep and cattle, then injected them with a virulent anthrax culture. All the vaccinated animals lived, while untreated animals died within three days.

Pasteur was even more famous for his rabies vaccine. After discovering that the disease was present in the central nervous system, Pasteur made an attenuated form of the virus from the dried nerve tissue of infected rabbits. On July 6, 1886, Pasteur administered his vaccine to a nine-year-old Joseph Meister, who had been bitten by a rabid dog; Meister made a full recovery.

In 1888, the Pasteur Institute was founded for the treatment of rabies and the study of infectious diseases, and as a center for learning. Pasteur was the institute's director until his death in 1895, and the institute remains a leading center for research, education, and public health today.

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