Cymbopogon martinii essential oil nanoemulsions: Physico-chemical characterization, antibacterial and antibiofilm potential against Enterococcus faecalis

Cymbopogon martinii is an aromatic crop cultivated for the production of its essential oil (EO) which has different applications. Bearing in mind that C. martinii EO (CMEO) has already been proved for high antibacterial potential the aim of this study was to formulate stable CMEO nanoemulsions, being capable to combat Enterococcus faecalis biofilm, especially within infected tooth's root canal. Ten emulsions with variable CMEO content (2.5-10 % v/v) and Tween 80 (T80, 2.5-15 % v/v) were formulated (designated as E-CMEO:T80) and screened for volume-weighted mean diameter (D4,3) and stability, using dynamic light scattering measurements. Chemical composition of stable nanoemulsions was monitored by UV-VIS and FTIR, while their antibacterial activity was estimated in microdilution assay. Antibiofilm properties of selected nanoemulsions were tested in vitro (cristal violet assay) and ex vivo (within root canals of the extracted teeth). Results showed that formulations containing 10 % of T80 and CMEO volume <= 6 %, as well as those having constant 2.5 % of CMEO and variable T80 volume (<= 10%), namely E-2.5:2.5, E-2.5:5, E-2.5:7.5, E-2.5:10, E-4:10, and E-6:10, were stable and nanosized (D4,3 <100 nm). FTIR and UV-VIS analyses confirmed successful encapsulation of the CMEO by T80 and showed that nanoemulsification did not affect CMEO composition. Evaluation of antibacterial potential showed that the most efficient were E-6:10, E-2.5:2.5 and E-4:10 (MIC values 0.37-1.97 mg mL(-1)). Analysis of dependency of determined MICs on mean diameter and CMEO volume showed that antibacterial potential increased with both parameters. E-6:10, E-2.5:2.5 and E-4:10 also reduced in vitro biofilm (inhibitory range 17.6-58.4 %), as well as intracanal biofilm (reduction similar to 2Log CFU). Presented results suggest E-6:10, E-4:10 and E-2.5:2.5 as the good candidates for further research.

Automated summary

This study successfully formulated stable nanoemulsions of Cymbopogon martinii essential oil (CMEO) and demonstrated their high antibacterial potential, especially against Enterococcus faecalis biofilm within infected tooth's root canal.