Investigation on inhibitory effect of tea pigments on mutans streptococci

Objective: To investigate the effect of tea pigments in inhibiting the growth, acid production and morphological changes of mutans streptococci. Methods: Two strains of mutans streptococci, S. mutans ingbritt and S. sobrinus 6715, were cultured in TSB medium containing 1% glucose. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of tea pigments containing 20%, 40% or 60% theaflavins and tea polyphenol containing 90% catechins for S. mutans were measured by two fold serial dilution. After S. mutans were cultured in TSB medium or in TSB medium with MIC of tea pigments of 40% theaflavins or tea polyphenol of 90% catechins at 37„aC for 24 h, the pH values of the bacterial supernatant/suspension were measured, respectively. After S. mutans were cultured in TSB medium or in TSB medium with the half concentration of MIC of tea pigments of 40% theaflavins or tea polyphenol of 90% catechins at 37„aC for 24 h, the bacterial morphology were observed by TEM. Results: Tea pigment of 40% theaflavin had the better inhibitory effect on the growth of S. mutans than tea pigments of 20% or 60% theaflavin, however, tea pigment (40%) had the similar inhibitory effect to the tea polyphenol of 90% catechins, with MIC and MBC of both being 2.5mg/ml and 5.0mg/ml respectively. Tea pigment (40%) and tea polyphenol (90%) could reduce acid production by S. mutans significantly (P<0.01). TEM findings revealed that tea pigment (40%) caused the vacuolar degeneration of cytoplasm of S. mutans, while tea polyphenols (90%) led to the destruction of cell membranes and abnormal shape of S. mutans. Conclusion: Tea pigments inhibited the growth and acid production of S. mutans by a synergistic action of the theaflavin with the other ingredients of tea pigments, and caused the vacuolar degeneration of cytoplasm of S. mutans.