Novel endophytic actinomycetes species Streptomyces panacea of Panax sokpayensis produce antimicrobial compounds against multidrug resistant Staphylococcus aureus.

Endophytic actinomycetes of medicinal plants have recently been in focus for developing novel antimicrobial compounds to combat multidrug-resistant pathogens. In this study, we isolated and characterised endophytic actinomycetes of Panax sokpayensis rhizome traditionally used as medicine in Sikkim-Himalayan region and assessed their antimicrobial activity against multidrug-resistant (MDR) clinical isolates of Staphylococcus aureus. Saccharopolyspora dominated as the endophytic actinomycetes of P. sokpayensis rhizome. However, a novel actinomycete strain PSRA5(T) belongs to the genus Streptomyces, with the highest genome sequence similarity of 91.54% with its closest relative Streptomyces niveus NCIMB 11891 has shown an effective inhibition of six clinical isolates of MDR S. aureus during disc diffusion assay. Further comparative analysis of cellular fatty acids composition and phenotypic and biochemical characteristics of strain PSRA5(T) with its phylogenetically closely related strain of S. niveus, classified as representing a novel species of the genus Streptomyces, for which the name Streptomyces panacea sp. nov. is proposed here with type strain PSRA5(T) (= MCC5238(T)). The minimum inhibition concentration of ethyl acetate crude extract of PSRA5(T) culture supernatant against MDR S. aureus isolates was 5.5 to 13.5 µg/mL. Further correlation between biosynthetic gene clusters identified by genome search with LC-MS analysis-based chemical profiling of PSRA5(T) culture extract and antibacterial activity of the representative compounds detected several compounds of aminoglycosides and polyketides with antimicrobial activity against MDR S. aureus isolates. Scanning electron microscope imaging viewed an interesting change in the S. aureus cell morphology with flocs of thread-like biofilm formation in response to the PSRA5(T) culture crude extract treatment. We conclude that the antimicrobial compounds produced by S. panacea PSRA5(T) can be further purified, characterised, and evaluated for their mode of action and efficacy against MDR S. aureus for developing novel drugs.