Chemical profile and antimicrobial potential of essential oils from the leaves and flowers of Syzygium ripicola (Craib) Merr. & L.M.Perry

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Syzygium ripicola (Craib) Merr. & L.M.Perry, a small tree species in the Myrtaceae family, is distributed in Southeast Asia, including Vietnam. This study investigates the chemical composition and antimicrobial activity of essential oils extracted from the leaves and flowers of S. ripicola. The leaf essential oil contained 55 compounds, primarily sesquiterpene hydrocarbons (46.09%) and monoterpene hydrocarbons (32.18%), with β-pinene (17.16%), (E)-caryophyllene (15.17%), and α-pinene (8.46%) as the major constituents. The flower essential oil comprised 33 compounds, predominantly monoterpene hydrocarbons (87.16%), with α-pinene (60.04%) and β-pinene (19.82%) being the most abundant. Both essential oils exhibited significant antimicrobial activity, particularly against Enterococcus faecalis (MIC = 32 μg/mL, IC50 = 12.35 μg/mL for leaf essential oil, 11.96 μg/mL for flower essential oil) and Staphylococcus aureus (MIC = 16 μg/mL, IC50 = 5.36 μg/mL for leaf essential oil, 6.01 μg/mL for flower essential oil), outperforming the positive control. The essential oils also inhibited Bacillus cereus (MIC = 32 μg/mL, IC50 = 10.86 μg/mL for leaf essential oil, 10.05 μg/mL for flower essential oil) and demonstrated potent antifungal activity against Candida albicans, with the leaf essential oil showing stronger efficacy (MIC = 1.6 μg/mL, IC50 = 5.64 μg/mL). However, neither essential oil was effective against Gram-negative bacteria, including Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica. These findings highlight the potential of S. ripicola essential oils as natural antimicrobial agents, particularly against Gram-positive bacteria and fungi.