In vitro inhibitory effects of rosemary extracts on growth and glucosyltransferase activity of Streptococcus sobrinus

Rosemary (Rosmarinus officinalis L.) extract functions as an antioxidant and antimicrobial agent. In this study, we investigated in vitro effects of rosemary extracts on Streptococcus sobrinus growth and on its extracellular glucosyltransferase activity. The antibacterial activities of rosemary extracts were determined by the microdilution broth method. The minimum inhibitory concentrations of aqueous and methanolic rosemary extracts against S. sobrinus were 16 and 4 mg/ml, respectively. Glucosyltransferase activity was tested by incubating a crude enzyme preparation with sucrose and determining the amount of water-insoluble glucan formed. Both aqueous and methanolic extracts of rosemary markedly inhibited the formation of water-insoluble glucan. The 50% inhibitory doses of aqueous and methanolic extracts against the glucosyltransferases of S. sobrinus were 1.42 mg/ml and 0.34 mg/ml, respectively. Our results suggest that rosemary extract may prove effective for the inhibition of the growth of cariogenic oral streptococci.