Chemical composition, antimicrobial and antioxidant activities of the essential oil and the ethanol extract of Cleistocalyx operculatus (Roxb.) Merr and Perry buds

In the present study, the essential oil isolated from the buds of Cleistocalyx operculatus by hydrodistillation was analyzed by GC and GC/MS. A total of 55 compounds representing 93.71% of the oil were identified. The oil significantly inhibited the growth of food spoilage (FS), food-borne (FB), skin pathogens (SP), methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococci (VRE) and multiantibiotic-resistant bacteria (MARB). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the oil against the tested microorganisms were found in the range of 1-20 μL/mL. Whereas the ethanol extract exhibited potential antibacterial activity against the entire tested Gram positive bacteria and one food spoilage Gram negative bacterium P. aeruginosa. The MIC and MBC values of ethanol extract against the tested bacteria were found in the range of 0.25-32 mg/mL. The scanning electron microscopic (SEM) studies demonstrated potential detrimental effect of the essential oil on the morphology of MRSA-P249 and VRE-B2332 at the used MIC values, along with the potential effect on cell viabilities of the tested bacteria. Moreover, the total antioxidant capacity and the scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals of the essential oil and the ethanol extract were also evaluated.