Composition development and in vitro evaluation of O/W emulsions based on natural emulsifier Olivem 1000 as tea tree oil carriers

The frequent occurrence of bacterial skin infections makes it necessary to search new solutions. Due to the limited effectiveness of traditional antibacterial agents, novel treatment alternatives are investigated. The use of plant origin compounds seems to be beneficial, because they are usually well tolerated and do not cause as many side effects as synthetic substances. Tea tree oil (TTO) is noted for well-established antimicrobial activity, so it can be used in the treatment of various skin diseases. It is effective against Gram-negative as well as Gram-positive bacteria. The aim of this work was to develop the composition and preparation technology of emulsion with TTO using natural emulsifier Olivem 1000 - combination of cetearyl olivate and sorbitan olivate. The designed formulations were evaluated by testing pH, stability and droplets size of the dispersed phase in the prepared emulsions. The type of emulsions was determined by selective phase staining method. In addition, rheological, mechanical, ex vivo bioadhesive properties of the prepared emulsions were studied and their antibacterial activity against selected strains was estimated. Obtained formulations were non-Newtonian systems, showing a shear-thinning behaviour and thixotropic properties, with proper textural features and beneficial bioadhesive properties. It was also demonstrated that formulations with lower viscosity showed higher antimicrobial efficacy against tested microorganisms and larger zones of inhibition were observed in case of Escherichia coli strains. The results of the study showed that the prepared emulsions appear to be a suitable form of topical administration of TTO.