Antibacterial, antioxidant and anti-inflammatory properties of essential oils in combination

Essential Oils (EOs) have long been used in folk medicine for their several biological properties. The increasing prevalence of antimicrobial resistance has led to their renewed interest as complementary agents for the treatment of drug-resistant human and veterinary infections. This study aimed to investigate novel binary combinations of EOs to explore their potential therapeutic applications. The research focused on antibacterial, antioxidant and anti-inflammatory properties of EOs derived from Origanum vulgare L. (Oregano), Juniperus communis L. (Juniper) and Cistus ladaniferus L. (Rock rose). The in vitro antibacterial properties of these EOs, alone and in combination, were investigated by the minimum inhibitory concentration (MIC) and checkerboard test against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), and Escherichia coli. The antioxidant capacity was evaluated using three redox-based assays: DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)), and FRAP (Ferric Reducing Antioxidant Power). The anti-inflammatory activity was assessed through the bovine serum albumin (BSA) denaturation inhibition assay. The results revealed that Oregano possesses the most potent antibacterial activity against all the strains tested with MIC values ranging from 0.0312% to 0.125% (v/v), and superior antioxidant and anti-inflammatory properties compared to the other EOs. For the combinations of Oregano/Rock rose and Oregano/Juniper, the calculation of fractional inhibitory concentration (FIC) allowed to highlight synergic and additive effects against S. aureus and MRSA, respectively. Moreover, the binary associations exhibited additive interaction in antioxidant and anti-inflammatory activities. In conclusion, the results suggest that the combinations of EOs may offer a promising strategy for treating S. aureus infections, including those caused by drug-resistant strains and associated with oxidative stress and inflammation. Further research is warranted to explore the efficacy, safety, and optimal formulations of these EO combinations for practical applications.