Synergistic Antimicrobial Effect of Lonicera japonica and Magnolia obovata Extracts and Potential as a Plant-Derived Natural Preservative

Most people use cosmetics to protect their skin. Preservatives are often used to prevent their contamination upon use. There has been a great demand for natural preservatives due to recent reports on the side effects of parabens. Therefore, we evaluated the antimicrobial activities of Lonicera japonica and Magnolia obovata extracts and determined their potential as natural preservatives. We found that the 50% ethanol extract from L. japonica had antibacterial activity only agains S. aureus and P. aeruginosa , while the ethyl acetate fraction showed antimicrobial activity against all six microbial strains tested. On the other hand, the 70% ethanol extract and the ethyl acetate fraction from M. obovata showed antimicrobial activity against all six strains. A synergistic effect agains S. aureus , B. subtilis , and C. albicans was confirmed when two ethyl acetate fractions having antimicrobial activity against all six strains were used in combination. Synergistic activity agains B. subtilis was also confirmed through kill-time analysis. High-performance liquid chromatography was performed to identify the components of each extract. Based on the minimum inhibitory concentration and the results of a disc diffusion assay, we confirmed that caffeic acid and luteolin influenced the antimicrobial activity of L. japonica and that the antimicrobial activity of M. obovata was influenced by the interaction of magnolol and honokiol with other components. Therefore, this study suggests that the combination of L. japonica and M. obovata extracts may be used as a plant-derived natural preservative.