Evaluation of the Preservative Properties of Origanum elongatum Essential Oil in a Topically Applied Formulation Under a Challenge Test

The aim of this study is to evaluate the preservative efficacy of Origanum elongatum essential oil in topical cream under a challenge test that was performed following the standard procedure proposed by the European Pharmacopoeia, using standardized microorganisms. Essential oil was analyzed by GC–MS (gas chromatography–mass spectrometry). The antimicrobial activity of this essential oil was investigated by agar diffusion methods and broth microdilution assay to determine the minimum inhibitory concentration of essential oil required for preservation. The results demonstrated that the preservation effect was effective at 2% (v/w) of Origanum elongatum essential oil in topical cream, satisfying criterion A against Staphylococcus aureus, Escherichia coli and Aspergillus brasiliensis. However, the essential oil was ineffective against Pseudomonas aeruginosa with a reduction of 102 within 7 days of challenge and no increase up to the 28th day and against Candida albicans in the challenge test. Carvacrol predominated (63.06%), followed by the two monoterpenes hydrocarbons: γ-terpinene (15.99%) and p-cymene (9.51%). Our study highlighted the preservative power of Origanum elongatum essential oil as an alternative solution to chemical preservatives.