Bifidobacteria and lactobacilli in human health.

The gastrointestinal microflora is a complex ecological system, normally characterized by a flexible equilibrium. The most important role of the microflora, from the point of view of the host, is probably to act in colonization resistance against exogenous, potentially pathogenic, microorganisms. Bifidobacteria and lactobacilli are Gram-positive lactic acid-producing bacteria constituting a major part of the intestinal microflora in humans and other mammals. Administration of antimicrobial agents may cause disturbances in the ecological balance of the gastrointestinal microflora with several unwanted effects such as colonization by potential pathogens. To maintain or reestablish the balance in the flora, supplements of intestinal microorganisms, mainly bifidobacteria and lactobacilli, sometimes called probiotics, have been successfully used. This article reviews the role of bifidobacteria and lactobacilli in human health.