Polyphasic characterization of a soil-derived Streptomyces sp. with activity against antimicrobial resistant Enterobacteriaceae

The global spread of antimicrobial resistance, particularly among Gram-negative pathogens, has intensified the search for novel bioactive compounds. Actinobacteria, especially members of the genus Streptomyces, remain a prolific source of antimicrobial metabolites. In this study, soil-derived actinobacterial isolates were characterized using a polyphasic taxonomic approach combining morphological, biochemical, and molecular analyses, followed by evaluation of antimicrobial activity against multidrug-resistant Gram-negative bacteria. Among the isolates, isolate LMA17 exhibited antibacterial activity against carbapenemase-producing Klebsiella pneumoniae and a multiresistant Escherichia coli strain. Morphological characterization based on the International Streptomyces Project revealed rectiflexibiles spore chains, while biochemical assays demonstrated broad metabolic versatility. Phylogenetic analysis of the 16S rRNA gene placed LMA17 within the genus Streptomyces, showing highest similarity to Streptomyces virginiae. Culture optimization assays indicated that yeast extract supplementation might have enhanced antimicrobial production. Activity-guided extraction suggested that the bioactive compounds are predominantly polar and cationic, consistent with streptothricin-like molecules. These findings support Streptomyces sp. LMA17 as a promising source of antimicrobial agents against carbapenem-resistant Enterobacteriaceae.