Selection criteria for probiotic microorganisms

Probiotics are preparations of live microorganisms which beneficially affect the host by improving the properties of the indigenous microbes. Since the human intestinal flora plays an important role in health and disease of man, probiotics are used to improve intestinal health and to stimulate the immune system. The microbes commonly used as probiotics for humans are the lactic acid bacteria (LAB). In early studies the strains used for fermenting milk products for human consumption were frequently used as probiotics. Subsequently, it was realised that it would be more appropriate if the strains originated from the human intestinal tract and that in addition to LABs, other microorganisms could be used either singly or in combination. Today, strict selection criteria are employed to obtain functional probiotic strains. It is generally agreed that the strain should be of host origin, well characterised, able to survive the rigours of the digestive tract and possibly colonise, biologically active against the target as well as to be stable and amenable to commercial production and distribution. In addition, information on dosages and evidence of efficacy needs to be obtained. In vitro and in vivo studies are frequently combined to allow investigation of the various parameters, and ultimately clinical trials are required. Although lactic acid bacteria have been generally recognised as safe, the question of safety is discussed for LAB and non-LAB probiotic strains in terms of potential pathogenicity of the strains and risk to the individual and the community. Finally, even though the techniques for genetic manipulation of many probiotic strains are available, it is not envisaged that this issue will be addressed in the near future because of regulatory implications. It is proposed that when this type of selection criteria is employed, probiotics strains with demonstrable efficacy can be obtained.