Objectives: This study aims to determine antimicrobial and anti-plaque effects of three essential oils against mutans streptococci. Methods: Three herbal essential oils as cinnamon (Cinnamomum zeylanicum), sweet basil (Ocimum basilicum) and peppermint (Mentha piperita) were tested for both antimicrobial and anti-plaque effects against Streptococcus mutans KPSK2. Inhibitory activity of these essential oils against such planktonic microbiota was examined via agar disc diffusion and broth micro-dilution methods. Both reducing and preventive effects of these herbs on S. mutan-biofilm were further investigated in vitro. Result: Minimum inhibitory concentration (MIC) value of each herb against tested microbe was identical to its minimum bactericidal concentration (MBC) value. The MICs and MBCs of cinnamon, sweet basil and peppermint were 0.08%, 1.25%, and 1.25% (v/v), respectively. At as less as their MBCs, all herbal essential oils demonstrated not only reduction but also preventive effect against S. mutans-biofilm. The established S. mutans-biofilm was reduced to 66.34±0.03%, 65.87±0.01% and 63.12±0.02% after exposed to the cinnamon, sweet basil and peppermint, respectively for 1 hour. Concomitantly, these herbs contained preventive effects by the formation of S. mutans-biofilm being reduced to 67.48±0.01, 58.13±0.01 and 55.55±0.01% after clean surfaces being primarily coated with cinnamon, sweet basil and peppermint, respectively for 1 hour. Furthermore, the longer the exposure time tested, the higher the reduction and preventive effects against the bacterial biofilm observed.
Conclusion: Cinnamon, sweet basil and peppermint expressed both antimicrobial and anti-plaque effects against both plantonic and biofilm forms of S. mutans