Isolation and Identification of Bioactive Compounds from Streptomyces actinomycinicus PJ85 and Their In Vitro Antimicrobial Activities against Methicillin-Resistant Staphylococcus aureus

Antibiotic-resistant strains are a global health-threatening problem. Drug-resistant microbes have compromised the control of infectious diseases. Therefore, the search for a novel class of antibiotic drugs is necessary. Streptomycetes have been described as the richest source of bioactive compounds, including antibiotics. This study was aimed to characterize the antibacterial compounds of Streptomyces sp. PJ85 isolated from dry dipterocarp forest soil in Northeast Thailand. The 16S rRNA gene sequence and phylogenetic analysis showed that PJ85 possessed a high similarity to Streptomyces actinomycinicus RCU-197(T) of 98.90%. The PJ85 strain was shown to produce antibacterial compounds that were active against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). The active compounds of PJ85 were extracted and purified using silica gel column chromatography. Two active antibacterial compounds, compound 1 and compound PJ85_F39, were purified and characterized with spectroscopy, including liquid chromatography and mass spectrometry (LC–MS). Compound 1 was identified as actinomycin D, and compound PJ85_F39 was identified as dihomo-γ-linolenic acid (DGLA). To the best of our knowledge, this is the first report of the purification and characterization of the antibacterial compounds of S. actinomycinicus.