Probiotics are living microorganisms that remain active in the gut in sufficient quantity to alter the host’s intestinal microbiota, both by implantation and colonization. They can have beneficial effects when ingested in sufficient quantities. They can pass through the digestive tract and recover alive in excreta, but also adhere to the intestinal mucosa.

In 2002, the World Health Organization (WHO) defined probiotics as “living microorganisms which, when supplied in adequate quantities, promote health benefits for the host organism”. Some preparations contain this kind of microorganisms and are therefore probiotic foods, fresh yoghurts, kefir, jocoque, sauerkraut, kimchi and many other lacto-fermented products. Although probiotics are considered safe, in some cases they can cause bacterial-host interactions and adverse side effects.

Genera, species and strains used as probiotics

Probiotic strains are identified by genus, species, subspecies (if applicable) and an alphanumeric designation identifying a particular strain. In the scientific community, there is agreement on the nomenclature applicable to microorganisms-for example, Lactobacillus casei DN-114 001 or Lactobacillus rhamnosus GG. Trade names are not controlled by the scientific community. According to WHO/FAO guidelines (, manufacturers of probiotics must register their strains with an international depository, which gives the strains an additional designation. In the case of probiotics it is important to use strain designations, as the most robust approach to probiotic evidence is to be able to attribute benefits to particular strains or combinations of probiotic strains at an effective dose.