**3. What are probiotics?**

The term 'probiotic' was proposed in 1965 to denote an organism or substance that contributes to the intestinal microbial balance. The definition of probiotics has subsequently evolved to emphasise a beneficial effect to health over effects on microbiota composition, underscoring the requirement of rigorously proven clinical efficacy. Most probiotic bacterial strains were originally isolated from the intestinal microbiota of healthy humans and the probiotics most thoroughly investigated thus far belong to the genera lactobacilli and bifidobacteria (Caramia G., 2004).

Probiotics have several effects, including modulating the gut microbiota, promoting mucosal barrier functions, inhibiting mucosal pathogen adherence and interacting with the innate and adaptive immune systems of the host, which may promote resistance against pathogens. The intestinal microbiota constitutes an important aspect of the mucosal barrier the function of which is to restrict mucosal colonisation by pathogens, to prevent pathogens from penetrating the mucosa and to initiate and regulate immune responses
