 Background In spite of the general decline in dental caries, early childhood caries ECC is still a severe global problem with social and behavioural gradients 1, 2. The disease is multi-factorial but the key event is a pH-induced stress in the oral environment that results in reduced diversity of the oral biofilm 3. The biofilm simply adapt to this situation with an overgrowth of caries-associated aciduric strains on behalf of beneficial and health promoting bacteria. Therefore, the addition of probiotic bacteria has been suggested as a novel approach to maintain oral health as an adjunct to the existing evidence-based methods 4, 5. Previous clinical trials have indicated that a daily intake of lactobacilli-derived dairy products can reduce caries incidence, improve general health and diminish the use of antibiotics in preschool children 6, 7, 8. However, further studies on the probiotic concept are needed; all children do not drink milk and no studies on childhood caries have hitherto been conducted with non-dairy products and streptococci strains. 