Antibacterial activity of oregano essential oils against Streptococcus mutans in vitro and analysis of active components

Abstract

AbstractBackgroundStreptococcus mutans(S. mutans) is considered the most relevant bacteria during the transition of the non-pathogenic commensal oral microbial community to plaque biofilms that promote the development of dental caries. Oregano (Origanum vulgareL.), is a universally natural flavoring and its essential oil has been demonstrated to have good antibacterial effects. However, the specific antibacterial mechanism of oregano essential oil (OEO) againstS. mutansis still not completely understood.MethodsIn this work, the composition of two different OEOs was determined by GC‒MS. Disk-diffusion method, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined to assess their antimicrobial effect onS. mutans. The inhibition of acid production, hydrophobicity, biofilm formation and real-time PCR forgtfB/C/D,spaP,gbpB,vicR,relAandbrpAmRNA expression byS. mutanswere assessed to preliminarily investigate the mechanisms of action. Molecular docking was performed to simulate the interactions with the virulence proteins and active constituents. MTT test using immortalized human keratinocytes cells was also performed to investigate cytotoxicity.ResultsCompared with the positive drug Penicillin /streptomycin 100X (DIZ: 34.13 ± 0.85 mm, MIC: 0.78125 μL/mL, MBC: 6.25 μL/mL), the essential oils ofOriganum vulgareL.(DIZ: 80 mm, MIC: 0.625μL/mL, MBC:2.5μL/mL) andOriganum heracleoticumL.(DIZ: 39.67 ± 0.81 mm, MIC: 0.625μL/mL, MBC: 1.25μL/mL) could also exhibit similar effects to inhibit the acid production and reduce the hydrophobicity and biofilm formation ofS. mutansat 1/2-1MIC concentration. And gene expression ofgtfB/C/D,spaP,gbpB,vicRandrelAwere found to be downregulated. Due to the composition of essential oils from different sources being highly variable, through effective network pharmacology analysis, we found that OEOs contained many effective compounds, like carvacrol and its biosynthetic precursorsγ-terpinene andp-cymene, which may directly target several virulence proteins ofS. mutans.Besides, no toxic effect was instigated by OEOs at 0.1 μL/mL in the immortalized human keratinocytes cells.ConclusionThe integrated analysis in the present study suggested that OEO might be a potential antibacterial agent for the prevention of dental caries.