Probiotics for Good Health
Probiotics are cultures of beneficial bacteria from the healthy gut microflora that improve the balance of the intestinal milieu by modifying the intestinal microflora and suppressing enhanced inflammatory responses. Probiotics are currently the subject of intense and widespread research as functional foods since they are known to induce health benefits, may be used as pharmaceutical preparations, and have achieved a "generally recognized as safe" (GRAS) status. Lactobacillus strains can also be genetically engineered for use in oral immunotherapeutic applications, such as vaccination and delivery of immunoregulatory substances. In the present review we evaluate the two different approaches to the therapeutic use of probiotics. We also focus on recent findings in the field of molecular biology and genetics of the intestinal immune response related to the microflora and intestinal, ecology, in order to understand the mechanisms of action of probiotics and their present indications in gastrointestinal diseases. Finally, with a view to future perspectives we provide some examples of probiotics that are being assessed and have great potential in improving the health of animals and man. © 2003 Prous Science. All rights reserved.
History of Probiotics
Since the early observations by Elie Metchnikoff (Fig. 1), the first scientist who proposed the therapeutic use of lactic acid bacteria (1), a wealth of experiments have described the use of selected microorganisms, mainly belonging to the lactic acid bacteria family, for the prevention or treatment of several pathological conditions (2).
Lactic acid bacteria were first discovered by Pasteur in 1857. Their isolation from rancid milk was reported in 1878 by Lister, and later they were also isolated from the intestinal tract. In 1889 Tissier discovered Bifidobacterium spp., and in 1900 Moro discovered Lactobacillus acidophilus (3). According to G. Reid (4) probiotics were first promoted for therapeutic relief of intestinal disorders in 1906 by Tissier in a thesis present at the University of Paris (5).
The first stable cultures of Lactobacillus casei strain Shirota were made in 1930 by Dr. Minoru Shirota (Fig. 2) at the Microbial Laboratory of the Faculty of Medicine at Kyoto University, in Japan. This organism was isolated from the human intestine; it is resistant to gastric acid and bile acid and can therefore reach the lower intestine after oral administration. In 1935, Dr. Shirota developed "Yakult", a dairy product manufactured using L. casei strain Shirota. He hypothesized that daily intake of this organism might promote intestinal health and prevent diseases, thereby prolonging lifespan (3). Several studies have shown that L. casei strain Shirota and dairy products manufactured using this strain have various biological activities. This had led to beneficial strains of L. casei strain Shirota and their products have been termed "probiotics".
The exact mechanisms underlying the proposed actions of lactic acid bacteria remain vastly unknown, partly due to the complexity of the gastrointestinal ecosystem in which these biotherapeutic agents interact, and to the increasing variety of strains with potential probiotic characteristics. During the past decades, the beneficial effects of specific strains in preventing or treating intestinal disorders have been assessed in well-controlled clinical trials. Increasing evidence, including human studies, also supports the immunomodulatory role of given lactic acid bacterial strains. Having acquired GRAS status, they have entered the field of immunoregulation of chronic inflammatory diseases and vaccination.