Endophytic actinobacteria from Mentha longifolia and Lonicera nummulariifolia: a novel source against antibiotic resistance.

backgroundThe escalating global challenge of antibiotic resistance severely restricts our ability to treat common infectious diseases, necessitating the urgent need for the development of novel antibiotics with distinct mechanisms of action. Actinobacteria, a diverse group of bacteria with medical, industrial, pharmaceutical, and ecological significance, produce approximately two-thirds of clinically used antibiotics. Endophytic actinobacteria (EA), residing within various plant species, represent a promising source for discovering novel antibiotics to combat this raising threat. This study aimed to explore the diversity and antibacterial characteristics of EA isolated from Mentha longifolia and Lonicera nummulariifolia, leveraging the host specificity and adaptation of EA to different plant species. Healthy plant samples were surface-sterilized and cultured on four distinct isolation media.

resultsNine EA isolates were identified from the roots, stems, and leaves of the plants based on morphological and molecular characterization. These isolates were taxonomically classified into two different families, Nocardiaceae and Streptomycetaceae, with Streptomyces being the dominant genus. All strains, except KUMS-B13, were reported as endophytes for the first time. Among the isolates, KUMS-B9 showed 98.66% sequence similarity to its closest relative strain, classifying it as a potential rare novel strain. The isolates exhibited diverse spore morphologies, including cylindrical, cubic, biconvex, oval, or ovoid shapes, with smooth or wrinkled surfaces. Six of the nine isolates displayed antibacterial activity against at least one of the tested bacteria: Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Isolate KUMS-B11, closely related to Streptomyces flavogriseus, showed broad-spectrum inhibition against all tested bacteria. Notably, a majority of the isolates demonstrated antagonistic activity against P. aeruginosa.

conclusionsThis study highlights EA isolated from Mentha longifolia and Lonicera nummulariifolia as a valuable source of medically bioactive metabolites with potential applications in human health. The isolation of new EA presents a promising approach to discovering novel therapeutic agents from unexplored ecological niches to battle antibiotic resistance. Furthermore, these findings emphasize the potential of plant-symbiotic bacteria in producing bioactive compounds with significant medicinal, pharmaceutical, and biotechnological applications.