Actinobacteria associated with medicinal plants are recognized as prolific sources of novel bioactive compounds. Kratom ( Mitragyna speciosa ) leaves have been reported to contain a diverse array of secondary metabolites with pharmacological activities, including antibacterial, antioxidant, and anti‐inflammatory effects. In this study, 16 actinobacterial isolates were successfully obtained from the leaves of M. speciosa . Based on the 16S rRNA gene sequence analysis, the isolates were identified as members of Streptomyces and non‐ Streptomyces genera, including Micromonospora , Pseudonocardia , Quadrisphaera , Prauserella , and Actinomycetospora . All isolates were screened for antibacterial activity, among which Micromonospora chersina NRAIS18 demonstrated notable inhibitory effects against both Gram‐positive and Gram‐negative pathogens. The ethyl acetate crude extract of NRAIS18 exhibited the most potent activity against Listeria monocytogenes ATCC 7644, followed by Pseudomonas aeruginosa ATCC 27853. Metabolomic profiling using LC‐MS and GC‐MS revealed diverse secondary metabolites in the crude extract, including the isoflavone daidzein, harman, norharman, and soyasaponin Bb; siderophores such as ferrioxamine E and desferrioxamine E; and other volatile bioactive compounds such as fatty acids, isoquinolines, and esters. Several of these metabolites have been reported to possess antibacterial properties. These findings suggest that M. chersina NRAIS18 demonstrates significant promise as a source of antibacterial agents for pharmaceutical applications.
Pitiwittayakul et al. (2026) studied this question.