Isolation and antibacterial evaluation of bioactive compounds from Mussaenda philippica A.Rich.: A bioassay-guided approach

Background: Mussaenda philippica A.Rich. (commonly known as Nusa Indah in Indonesia), a member of the Rubiaceae family, has been traditionally used throughout Southern Asia to treat various ailments, including bacterial infections, inflammation, ulcers, and liver disorders. These medicinal uses are particularly associated with its bark, leaves, sepals, and root. Objectives: This study aimed to isolate and identify bioactive compounds from M. philippica white modified sepals using a bioassay-guided approach and evaluate their antibacterial activity. Materials and Methods: The study consisted of four main stages: (i) methanol extraction and liquid–liquid partitioning of M. philippica sepals; (ii) bioassay-guided isolation of the ethyl fraction by column chromatography; (iii) structural characterization of the isolated compounds; and (iv) evaluation of their antibacterial activity. Antibacterial testing was performed using the microdilution method to determine the minimum inhibitory concentration (MIC) of isolated compounds against six bacterial strains: Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, Staphylococcus epidermidis ATCC 12228, Salmonella typhimurium ATCC 14028, Escherichia coli ATCC 25922, and Vibrio cholerae Inaba. Results: Two compounds were isolated and identified, each exhibiting distinct antimicrobial activity profiles against the tested bacterial strains. Compound 1, identified as isoquercitrin, showed MIC values ranging from 28.12 μg/mL (against S. epidermidis and E. coli) to 62.5 μg/mL (against S. aureus), while 2, tentatively identified as astragalin, displayed MIC values between 21.87 μg/mL (against E. coli and V. cholerae) and 125 μg/mL (against S. aureus). Conclusion: This study successfully employed a bioassay-guided approach to isolate and identify bioactive compounds from the sepals of M. philippica, which exhibited preferential antibacterial activity against Gram-negative bacteria. These findings provide evidence of the antibacterial potential of M. philippica and may lead to further investigation.