Antibacterial Properties of Endophytic Bacteria Isolated from Kalimantan’s Kratom (Mitragyna speciosa)

Abstract

As the ongoing battle against the escalating challenge of antibiotic resistance persists, pursuing alternative reservoirs for antimicrobial agents becomes crucial. Endophytic bacteria have surfaced as promising contenders for novel antibacterial compounds. Due to the increasing popularity of kratom (Mitragyna speciosa), the Indonesian government encourages the study of potential pharmaceutical properties of the plant. Therefore, this research aimed to explore the antibacterial activity of 17 isolated endophytic bacteria from the leaf and stem of kratom against common bacteria. This is an initial effort to identify potential bacterial candidates that can produce bioactive compounds capable of inhibiting the growth of antibiotic-resistant bacteria. Among the 17 endophytic bacteria, two coded as KB6 and KB9 exhibited antibacterial activity. However, KB6 extract possessed higher antibacterial activity against Bacillus subtilis (ATCC 6633) and Staphylococcus aureus (ATCC 25923), as demonstrated by greater inhibition zones, lower minimum inhibitory concentration, and minimum bactericidal concentration. Further GC-MS analysis showed that the KB6 crude extract contained 50 compounds with numerous identities. Interestingly, several compounds, including mesitylene, previously reported as a potential antibacterial compound, were also detected. Molecular studies and microscopy technique confirmed the identity of KB6 as belonging to the genus Bacillus. The bacterium's ability to produce antibacterial compounds was also confirmed by the presence of the polyketide synthase type I gene, which is crucial in the biosynthetic pathways of secondary metabolites. The results of this study implied the potential of endophytic bacteria from kratom as a reservoir of antibacterial compounds, encouraging a broader scope in antibiotic research.