Probiotics are live microbial preparations, which have documented health benefits for the consumers by maintaining or improving their intestinal microbiota balance. Established probiotic effects include improved lactose digestion, modulation of gut microbiota, immune modulation, reduced duration of rotavirus diarrhoea, changes in biomarkers such as harmful faecal enzyme activities, alleviation of atopic dermatitis symptoms in babies, and positive effects against superficial bladder cancer and cervical cancer. Most bacteria that have probiotic properties belong to the genera Lactobacillus and Bifidobacterium. Since probiotic consumption involves ingestion of large numbers of viable bacterial cells (daily dosage between log r 9 and log r 11 CFU) safety aspects of probiotic consumption are of utmost importance. Knowledge on the survival of probiotics in the GI-tract, their translocation and colonisation properties and the fate of probiotic-derived active components is important for the evaluation of possible negative and positive effects of probiotic consumption. Assessing the risks of probiotic consumption can be a very expensive and time-consuming task. While considering the risk of probiotic consumption we have to keep in mind that lactic acid bacteria have been globally consumed in a myriad of fermented food varieties (milk, meat, vegetable and cereal products) for a very long time without an indication that they could be generally harmful to the consumers' health. In Finland lactobacilli strains isolated from bacteremia have been systematically characterised. Although the yearly consumption of probiotic products containing lactobacilli has increased during the last 10 years, the incidence of lactobacillemia has not increased. There is one local infection case with an indistinguishable isolate to L. rhamnosus GG. The extensive follow-up period indicates that the risk of serious infection by one single probiotic strain is very low. Simultaneously, it is difficult to estimate all the health benefits the same probiotic strain has implemented, also in immunocompromised patients. However, no live bacterium can be guaranteed for a zero risk in each individual host since the outcome of bacterial ingestion (passage through GI-tract, colonisation, infection) is determined both by the host and the bacterium.
Saarela, M., Mättö, J., & Mattila-Sandholm, T. (2002). Safety aspects of Lsctobacillus and Bifidobacterium species originating from human oro-gastrointestinal tract or from probiotic products. Microbial Ecology in Health and Disease, 14(4), 234-241. https://doi.org/10.1080/08910600310002127