chemical composition and antibacterial activity of some herbal essential oils against streptococcus mutans

background and aims: one of the most common chronic diseases in the world is tooth decay. a variety of bacteria are involved in this disorder of which streptococcus mutants is the most common. essential oils are considered as new natural compounds for use in combating drug-resistant bacteria. this study was aimed to evaluate the antibacterial activity of some essential oils prepared from eucalyptus caesia benth, cuminum cyminum l. and satureja hortensis l. on s. mutants. methods: in this study, essential oils were extracted by hydrodistillation method. e. caesia benth, c. cyminum l. and s. hortensis l. were characterized by using gas chromatography‒mass spectrophotometry (gc‒ms). antibacterial activity indices including minimum inhibitory concentration (mic), minimum bactericidal concentration (mbc) and zone of inhibition for the above essential oils against streptococcus mutans were determined using broth macro-dilution and disk diffusion methods. data analysis was performed using one-way anova and tukey test. results:results showed that all three extracts had antibacterial activity against s. mutants. s. hortensis l. essential oil with the lowest mic and mbc value (13.2 and 18.4 µg/ml, respectively) and the biggest inhibition zone showed the strongest antibacterial effect against s. mutants in all exposure times and at all concentrations, compared with two other essential oils. furthermore, c. cyminum l. essential oil had higher anti-bacterial activity against s. mutant than e. caesia benth essential oil. conclusions:the essential oils used in the present study with different components showed antibacterial activity (especially s. hortensis l essential oil), and therefore they can be used as a new antibacterial substance.   keywords: dental caries, streptococcus mutans, essential oils, antimicrobial.