Antioxidant activity and synergistic antimicrobial effects of Acorus calamus and Hedychium spicatum essential oil with conventional antibiotics

The antioxidant, antimicrobial properties, and chemical composition of essential oil extracted from Hedychium spicatum and Acorus calamus aromatic plants was estimated. The primary constituents found in the essential oils were eucalyptol (22.43%) in H. spicatum and β-asarone (83.45%) in A. calamus. The essential oil of A. calamus demonstrated greater antioxidant activity than that of H. spicatum, as shown by its higher DPPH free radical scavenging activity (IC₅₀ value:1.00 ± 0.016 mg/mL), reducing power (IC₅₀ value: 4.54 ± 0.008 mg/mL), and FRAP activity (150.23 ± 6.07 mM Fe²⁺eq./100 mg). Both essential oils showed notable antimicrobial activity having inhibition zones ranging from 11 ± 0.75 to 13.5 ± 0.87 mm for H. spicatum and 8 ± 0.45 to 14.5 ± 0.87 mm for A. calamus against various Gram-negative bacteria, including Klebsiella pneumoniae (K.p.), Escherichia coli (E.c.) and Gram-positive bacteria, such as Bacillus subtilis (B.s.), Staphylococcus aureus (S.a.), and Micrococcus luteus (M.l.). Furthermore, the essential oils' minimum inhibitory concentrations against the studied microorganisms varied from 900 to 3100 µg/mL. Studies combining synthetic antibiotics with essential oils revealed synergistic and partially synergistic interactions, indicating that essential oils can increase the effectiveness of antibiotics against bacteria that are resistant to several drugs. Finally, the essential oils of A. calamus and H. spicatum show encouraging antioxidant and antibacterial properties, underscoring their potential as natural therapies for microbial diseases and lowering dependency on synthetic antibiotics.