Antibacterial, antioxidant activities and phytochemistry of Bruguiera gymnorrhiza stem using LC-ESI-QTOF-MS/MS

Bruguiera gymnorrhiza is a therapeutically important mangrove species whose phytochemistry and associated bioactivities remain underexplored. This study aimed to explore the bioactive potential of crude extracts of the B. gymnorrhiza plant stem through antibacterial (disc diffusion assay and minimum inhibitory concentration), antioxidant (DPPH and ABTS radical scavenging activities), and phytochemical evaluation using LC-ESI-QTOF-MS/MS profiling. Stem ethyl acetate (BGEA) and chloroform (BGC) extracts of B. gymnorrhiza solvents showed maximum effectiveness against all tested microorganisms in a concentration-dependent manner. The stem ethyl acetate and chloroform extracts exhibited the strongest inhibition against Gram negative Klebsiella pneumoniae and Salmonella typhimurium with ZOI of 30 mm and 29.7 mm, respectively. The MIC assay revealed the BGC extract achieved the lowest MIC values across almost all tested organisms. Antioxidant assays revealed moderate activity in DPPH radical scavenging by the chloroform extract (IC₅₀ = 641.6 µg mL⁻¹), whereas the ethyl acetate extract was more effective out of the tested extracts in the ABTS assay (IC₅₀ = 440.5 µg mL⁻¹). LC-ESI-QTOF-MS/MS profiling identified 51 metabolites tentatively belonging to major classes such as flavonoids, fatty acids, terpenoids, carboxylic acids, phenolic acids, quinones, and alkaloids. The phytocompounds detected included apigenin, quercetin, glycitein, abscisic acid, 18-β-glycyrrhetinic acid, chlorogenic and caffeoylquinic acids, tetrahydrocortisone, β-oestradiol, hesperetin, phenolic glycosides, and several coumarins. Therefore, the stem extracts derived using ethyl acetate and chloroform exhibited notable antibacterial and antioxidant activities. These findings suggest B. gymnorrhiza stem extracts may be renewable sources of phytochemicals for developing plant-based therapeutics against multidrug-resistant bacteria.