Chemical Composition, Synergistic Antimicrobial and Antioxidant Potential of <i>Hibiscus rosa-sinensis</i> L. Leaves Essential Oil and Its Major Compound

This study aimed to investigate the chemical composition, antioxidant and synergistic antimicrobial potential of <i>Hibiscus rosa-sinensis</i> L. (China rose) leaves essential oil and its major compound, Dioctyl phthalate (DOP). The essential oil was extracted from leaves by hydro-distillation using the Clevenger apparatus. The essential oil was characterized by Gas Chromatography-Mass Spectrometry (GC/MS) analysis which revealed the presence of DOP as a major compound. The essential oil and DOP were tested for antibacterial activity against <i>Klebsiella</i> sp. and <i>Pseudomonas aeruginosa</i> using the disc plate method, antifungal activity against <i>Fusarium oxysporum</i> by agar well diffusion method, and antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) free radical scavenging assays. The synergistic antimicrobial interaction of essential oil and DOP was also tested against standard antimicrobials: tetracycline, chloramphenicol, fluconazole, and clotrimazole. The maximum antimicrobial potential was exhibited by China rose leaves essential oil with minimum inhibitory concentrations (MIC) of 18.5, 11.5, and 23.0 μg/mL against <i>Klebsiella</i> sp.<i>, P. aeruginosa</i>, and <i>F</i>. <i>oxysporum</i> respectively. Moreover, the essential oil exhibited synergistic interaction with standard antimicrobials with a 3.75 to 10 times decrease in their MIC values. The essential oil also exhibited median inhibitory concentration (IC₅₀) values of 780, 800, and 860 μg/mL in DPPH, NO, and ABTS free radical scavenging assays respectively. Hence it can be concluded that China rose leaves essential oil has a huge significance in pharmaceutical industries as an alternative to synthetic antioxidants and antimicrobials in near future.