The Biology Book: From the Origin of Life to Epigenetics, 250 Milestones in the History of Biology (2015)


Élie Metchnikoff (1845–1916), Minoru Shirota (1899–1982)


The human body is home to more than 100 trillion bacteria, with a total weight of five pounds; the mouth alone houses several hundred bacterial species. In the past, bacteria were exclusively associated with infectious diseases, often with fatal consequences, and in cases of food poisoning. Modern medicine has compounded this problem with the overuse of antibiotics that nonselectively rid the body of harmful microbes, as well as those that provide benefit. This is particularly true in the intestinal tract, where the use of broad-spectrum antibiotics disrupts the normal microbial balance in the gut, causing diarrhea.

THE GOOD BACTERIA. In 1907, the Russian biologist Élie Metchnikoff, who was a co-recipient of the 1907 Nobel Prize for immunity research, conceived of the notion that it was possible to modify the gut flora and replace harmful microbes with beneficial ones. More specifically, fermented milk could “seed” the intestines with lactobacillus, which would acidify the intestines and suppress the growth of these proteolytic bacteria (bacteria that break down proteins). Metchnikoff attributed the aging process to the accumulation of waste materials in the lower segment of the large intestines that empties into the rectum, and the leaking back of these toxic substances from the rectum into the bloodstream (known as autointoxication). Metchnikoff noted that the rural population of Bulgaria, who subsisted primarily on milk fermented with lactobaccilus (lactic acid bacteria), was exceptionally long-lived.

During the 1930s, Minoru Shirota in Japan, inspired by Metchnikoff’s concepts, developed Yakult, a yogurt-like drink containing a stronger strain of lactobacillus that was intended to destroy harmful intestinal bacteria. This product, and others like it that have been introduced in recent years, are referred to as probiotics, which are simply living microbes used as food supplements. They benefit the user by improving the intestinal microbial balance.

Although many health claims have been made for probiotics, from curing intestinal disorders to a very wide range of major systemic disorders, to date no claim for medical use has been approved by the Food and Drug Administration or the European Food Safety Authority.

SEE ALSO: Prokaryotes (c. 3.9 Billion BCE), Microbial Fermentation (1857), Antibiotics (1928).

Balkan yogurt differs from Greek and Swiss styles because it is allowed to ferment inside individual containers rather than in large vats. The image depicts Balkan homemade yogurt—a great source of probiotics—served in a traditional ceramic dish.