Probiotic foods – a fad with facts

Bacteria have generally been perceived as unwelcome harbingers of disease and decay, although antibiotics and improved sanitation have done much to reduce their harmful effects. A dietary trend is now emerging where ‘friendly’ probiotic bacteria are eaten, in capsules or in other foods for their health benefits. This has attracted attention in the US media, and, unlike some food fads, has scientific support. Probiotic microbes such as Lactobacillus and Bifidobacterium naturally inhabit our intestines. They protect us from pathogens, aid lactose digestion and can alleviate inflammatory bowel disease. In a further development, engineered probiotic bacteria overexpressing the cytokine interleukin-10 improved colitis in experimental mice [Science 289, p. 131 (2000)].The health benefits of probiotic foods have long been recognized. In 1908, Metchnikoff suggested that consumption of natural yoghurt was responsible for the longevity of Russian peasants. Nowadays though, our food is mostly pasteurized, and we are just starting to understand the importance of bacteria to our health. Surprisingly little is known about our interaction with the bacterial world, as illustrated by the work of Norman Pace (Boulder, Colorado) who, from PCR-based methods, estimates ‘99% of organisms seen microscopically are not cultivated by routine techniques and are yet to be characterized’. In addition, several new intestinal bacteria have recently been discovered [J. Appl. Microbiol. p. 551 (2000)], suggesting that the murky world of microbes still holds many interesting secrets. S.L.