Designing an ideal essential oil combination nanoemulsion formulation for the management of respiratory tract infections

Essential oils are well studied for their antimicrobial effects; however, blends extending to formulations are rarely scientifically explored. In this study, we aimed to quantify and optimise the synergy of an essential oil blend by means of computational interpretation in order to create a nanoemulsion formulation ideal for use against respiratory tract pathogens. The nanoemulsion blend consisted of essential oils from Hyssopus officinalis var. angustifolius in combination with Salvia rosmarinus var. angustifolius. The prediction tool SynergyFinder (Version 2.0) was implemented to determine optimal synergy blends. According to the synergy maps derived, an optimal blend of these two essential oils is composed of 49.57% of H. officinalis and 50.43% of S. rosmarinus. This optimised blend was then formulated into a nanoemulsion, using the two-component, self-emulsification technique. The essential oil nanoemulsion showed strong in vitro antimicrobial activities against pathogens of the respiratory tract including Streptococcus pneumoniae (ATCC 49619), Haemophilus influenzae (ATCC 19418), Klebsiella pneumoniae (ATCC 13883) and Moraxella catarrhalis (ATCC 23246), with an average six-fold improvement in antimicrobial effect when compared to the neat essential oils. The blended H. officinalis and S. rosmarinus essential oil nanoemulsion therefore holds potential to be developed as a natural antimicrobial agent for the management of respiratory tract infections.