Probiotics are live microorganisms, usually bacteria, that can be consumed to offer health benefits.

The ability of certain microbes to confer health benefits on their host was recognized more than 100 years ago. In 1904, Elie Metchnikoff, a scientist at the Pasteur Institute, claimed that Bulgarian peasants lived longer by eating yogurt made from bacteria that served to ferment the milk. Parisians rushed out to buy yogurt in response.

However, the huge variety of bacteria living on the planet was not appreciated back then. More recently, the development of technology that identifies organisms from their DNA has allowed scientists to show that plants, animals, insects and humans can be hosts for many different types of microorganisms.