Thymol and carvacrol induce autolysis, stress, growth inhibition and reduce the biofilm formation by Streptococcus mutans.
Khan ST1,2, Khan M3, Ahmad J4,5, Wahab R4,5, Abd-Elkader OH5, Musarrat J6, Alkhathlan HZ7, Al-Kedhairy AA4
1,4Zoology Department, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
2,5DNA Research Chair, Zoology Department, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
3Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
6Department of Ag. Microbiology, Faculty of Agricultural Sciences, AMU, Aligarh, 202002, India.
7Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
Organic compounds from plants are an attractive alternative to conventional antimicrobial agents. Therefore, two compounds namely M-1 and M-2 were purified from Origanum vulgare L. and were identified as carvacrol and thymol, respectively. Antimicrobial and antibiofilm activities of these compounds along with chlorhexidine digluconate using various assays was determined against dental caries causing bacteria Streptococcus mutans. The IC50 values of carvacrol (M-1) and thymol (M-2) against Streptococcus mutans were 65 and 54 µg/ml, respectively. Live and dead staining and the MTT assays reveal that a concentration of 100 µg/ml of these compounds reduced the viability and the metabolic activity of Streptococcus mutans by more than 50%. Biofilm formation on the surface of polystyrene plates was significantly reduced by M-1 and M-2 at 100 µg/ml as observed under scanning electron microscope and by colorimetric assay. These results were in agreement with RT-PCR studies. Wherein exposure to 25 µg/ml of M-1 and M-2 showed a 2.2 and 2.4-fold increase in Autolysin gene (AtlE) expression level, respectively. While an increase of 1.3 and 1.4 fold was observed in the super oxide dismutase gene (sodA) activity with the same concentrations of M-1 and M-2, respectively. An increase in the ymcA gene and a decrease in the gtfB gene expression levels was observed following the treatment with M-1 and M-2. These results strongly suggest that carvacrol and thymol isolated from O. vulgare L. exhibit good bactericidal and antibiofilm activity against S. mutans and can be used as a green alternative to control dental caries.
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