Objective  To examine the in vitro inhibitory effect of flower extracts from Salvia deserta Schang (SFE) on Streptococcu smutans (S. mutans).

  Methods  The inhibitory effect of SFE on planktonic S. mutans and the effect of SFE on the growth process of planktonic S. mutans were determined by the agar drilling method and the microdilution method. Crystal violet staining and MTT reduction assay were conducted to determine the effect of SFE on S. mutans biofilm formation. The effect of SFE on the production of exopolysaccharides (EPS) in S. mutans biofilm was determined by anthrone-sulfuric acid method. The intracellular lactate dehydrogenase (LDH) activity in S. mutans was determined by LDH colorimetric assay. The effects of SFE on the acid-producing capacity of S. mutans was determined by pH meter.

  Results  The minimum inhibitory concentration (MIC) of SFE against S. mutans was 14 μg/μL. SFE of the the concentration between 1/8 MIC and MIC could inhibit the growth rate of S. mutans within 30 h and it could significantly inhibit the LDH activity compared with the control group (P<0.0001). SFE of the concentration between 4 MIC and 1/4 MIC had an inhibitory effect on the acid production of S. mutans (P<0.001). Moreover, it could effectively restrain the formation of S. mutans biofilm and significantly reduce the amount of EPS produced by biofilm (P<0.01).

  Conclusion  SFE can effectively inhibit the activity of S. mutans and its biofilm. The mechanism of inhibiting S. mutans by SFE was preliminarily discussed as follows, it interferes with microbial adhesion and aggregation by reducing the production of bacterial EPS, thus inhibiting the formation of bacterial biofilms. In addition, it interferes with glycolysis of S. mutans by reducing the LDH activity of bacteria, thus inhibiting the acid production of S. mutans.