Preservative efficacy of the combination of essential oils of Cymbopogon citratus (DC.) Stapf (Poaceae) and Citrus sinensis (l.) Osbeck (Rutaceae) in a cream formulation

Background: The search for so called green chemicals is on the increase. This is particularly important in antimicrobials, given the current trend in the development of antimicrobial resistance and the questions concerning the possible carcinogenic effect of traditional cosmetic preservatives like the parabens. Objectives: This study is aimed at investigating the combined antimicrobial properties of essential oils extracted from Cymbopogon citratus and Citrus sinensis peels, and to evaluate their preservative efficacy in aqueous creams.

Methods: The essential oils were obtained by steam distillation. Their antibacterial and antifungal activities were evaluated using the disc agar diffusion method while their minimum inhibitory concentrations (MIC) were determined by the agar dilution method. The combined antimicrobial effects of the essential oils were also evaluated using a modified checkerboard method. Various decimal combinations of the oils were included informulatedcreams, and the physicochemical and microbiological stability (preservative activities) of the creams assayed.

Results: Antimicrobial screening showed thatC. citratus and C. sinensis both had strong antifungal activities against the species tested but have variable antibacterial activities against different bacterial species. All the decimal combinations of the essential oils had synergistic effects against the studied bacteria as shown by the fractional inhibitory concentration (FIC) index against the various test isolates. The results of the challenge tests revealed that the oils produced significant reduction of the microbial inocula, satisfying the criterion A of the European Pharmacopoeia.

Conclusions: Due to the stability and preservative efficacy of essential oils of C. citratus and C. sinensis, they could be useful adjuvants in creams for topical application as antimicrobial agent to minimize microbial contamination caused by these organisms in multidose cream formulations.