Probiotics: how should they be defined?

Probiotics have been defined in several ways, depending on our understanding of the mechanisms of action of their effects on health and well-being of humans. The term probiotic was coined by Lilly and Stillwell to describe substances produced by one microorganism, that stimulate the growth of another, thus meaning the opposite of antibiotics. Parker subsequently defined probiotics as organisms and substances that contribute to intestinal balance. This definition, however, did not exclude antibiotics. At present, the most commonly used definition is that of Fuller: Probiotics are live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance. Recently a European expert group widened the definition to include mechanisms other than just microflora mediated ones. The definition was as follows: Probiotics are live microbial food ingredients that have a beneficial effect on human health. To include the current application and scientific data on proven effects of probiotics we propose the following definition: Probiotics are microbial cell preparations or components of microbial cells that have a beneficial effect on the health and well-being of the host. This definition implies that probiotics do not necessarily need to be viable. Non-viable forms of probiotics have also been shown to have health effects. The definition does not restrict the use of probiotics in foods; several other applications have been reported to have beneficial health effects. Not only whole microbial cells, but also parts of cells have been observed to improve host health. Metabolites are, however, not included in the current definition. Thus, it excludes antibiotics. The proposed definition is based on the mechanisms of action, selection criteria, viability and non-viability, and scientifically documented health effects that will be discussed.