Probiotics have been a subject of interest among the scientific community since the beginning of the twentieth century. More than a century ago, Russian scientist and Nobel laureate Elie Metchnikoff first introduced the concept that the gut flora can be modified and harmful microbes replaced with beneficial ones to confer health benefits.

Metchnikoff proposed the idea that “intestinal auto-intoxication” is caused by putrefactive or proteolytic bacteria that generate toxins in the large bowel. He described how the proteolytic bacteria, clostridia, that exist as part of the gut flora produce toxic substances such as phenols and ammonia through the digestion of proteins. He believed that this intestinal auto-intoxication could contribute to the aging process, but that this process could be suppressed by modifying the gut flora to replace harmful microbes with beneficial ones.

Metchnikoff suggested that drinking fermented milk would establish harmless bacteria in the gut and decrease the pH, providing an environment in which the growth of proteolytic bacteria would be suppressed. The scientist began himself to drink milk fermented with “Bulgarian Bacillus” and reported that his health did benefit. This led to physicians eventually prescribing the fermented milk to their patients.

In 1917, during a shigellosis outbreak, German professor Alfred Nissle isolated a strain of Eschericia coli from a soldier who was not affected by the disease. He then used this to treat people suffering from shigellosis and acute gastrointestinal salmonellosis.

Henry Tissier of the Pasteur Institute isolated another important probiotic bacteria called Bifidobacterium, which is dominant in the intestinal flora of breast-fed babies. He originally called it Bacillus bifidus communi. Tissier noticed that the bacteria conferred clinical benefits when used to treat diarrhea in babies, an effect that was claimed to be due to the displacement of proteolytic bacteria that were causing the disease.