inhibits the acid tolerance response in oral bacteria.

Probiotic bacteria show promising results in prevention of the biofilm-mediated disease caries, but the mechanisms are not fully understood. The acid tolerance response (ATR) allows biofilm bacteria to survive and metabolize at low pH resulting from microbial carbohydrate fermentation. We have studied the effect of probiotic strains: and on ATR induction in common oral bacteria. Communities of L. ATCC PTA5289 and or in the initial stages of biofilm formation were exposed to pH 5.5 to allow ATR induction, followed by a low pH challenge. Acid tolerance was evaluated as viable cells after staining with LIVE/DEAD®BacLight™. The presence of ATCC PTA5289 caused a significant reduction in acid tolerance in all strains except . When was used as a model organism to study the effects of additional probiotic strains ( SD2112, DSM17938 or GG) as well as ATCC PTA5289 supernatant on ATR development, neither the other probiotic strains nor supernatants showed any effect. The presence of ATCC PTA5289 during ATR induction led to down-regulation of three key genes involved in tolerance of acid stress (, and ) in Streptococci. These data suggest that live cells of probiotic ATCC PTA5289 can interfere with ATR development in common oral bacteria and specific strains of may thus have a role in caries prevention by inhibiting development of an acid-tolerant biofilm microbiota.