Characterization of Streptococcus salivarius growth and maintenance in artificial saliva

Aims: To help gain a better understanding of factors influencing the establishment within the oral cavity of Streptococcus salivarius K12, a commensal oral bacterium, we characterized its behaviour in artificial saliva. Methods and Results: Streptococcus salivarius K12 was grown in artificial saliva complemented with a representative meal, under oral pH and temperature conditions. Exponential growth phase was characterized by a high specific growth rate (2.8 h(-1)). During maintenance phase, an uncoupling between growth and lactic acid production occurred, which allowed maintaining viability (95%), intracellular pH (6.6) and membrane polarisation (95%), and thus proton motive force. However, in late stationary phase, viability (64%) and vitality were degraded as a result of lower synthesis of energetic and glycogen-related proteins as compared to a richer medium. Conclusions: Streptococcus salivarius was able to rapidly grow in complemented artificial saliva. Nevertheless, a degradation of its physiological state was observed in late-stationary phase. Significance and Impact of the Study: This work demonstrates, for the first time, that artificial saliva was a convenient medium that permitted Strep. salivarius to grow in oral conditions (physico-chemical environment, addition of meals) but not to maintain cellular viability and vitality in starvation conditions.