Exploring northeast India's culturable soil Actinomycetia for potent antibacterial agents against gram-positive bacterial pathogens of clinical importance.

This study investigated the isolation and bioactivity of Actinomycetia from the soil of Northeast India, a region rich in microbial diversity. A total of 187 presumptive Actinomycetia isolates were obtained and 53 were found to exhibit antimicrobial properties. Phylogenetic analysis based on 16 S rRNA gene sequencing revealed that the isolates were predominantly from the genus Streptomyces. Among these, the strain Streptomyces sp. NP14 (ANP14ARS) demonstrated specific and significant antimicrobial activity against gram-positive bacterial pathogens. The strain was further assayed against a panel of clinically important bacterial pathogens including Methicillin-resistant Staphylococcus aureus (MRSA). Its antimicrobial activity was confirmed using disc diffusion and membrane disruption assay, and its minimum inhibitory concentration was determined to be ≥ 3.12 ± 0.5 µg/ml against MRSA. Chemical analyses using FTIR and GC-MS identified key bioactive compounds, including Pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)- and Phenol 3,5-bis(1,1-dimethylethyl), known for their antimicrobial properties. Toxicity studies against animal liver cell lines indicated that the ethyl acetate extract was non-toxic at concentrations below 125 µg/mL, compared to Vancomycin, which was found to be hepatotoxic at similar concentrations. These findings highlight the potential of ANP14ARS as a source of bioactive natural products that is specific towards priority pathogens such as MRSA.