Bioactive Metabolites from Streptomyces mutabilis PQ668646: Purification, Characterization, and Antibacterial and Antibiofilm Activities Against MRSA with Anticancer Potential

Abstract

The escalating prevalence of methicillin-resistant Staphylococcus aureus (MRSA) underscores the critical need
for novel antimicrobial agents capable of circumventing established resistance mechanisms. Actinomycetes,
particularly Streptomyces species, remain one of the most prolific sources of clinically relevant natural antibiotics
and represent a promising reservoir for new therapeutic compounds. In this study, we evaluated the antimicro
bial and antibiofilm potential of actinomycete-derived metabolites against clinical MRSA isolates to identify
candidates with translational potential for managing persistent and device-associated infections. A total of 165 Staphylococcus isolates were recovered from diverse clinical specimens and confirmed phenotypically as MRSA through standard microbiological and  antimicrobial susceptibility assays. Ten actinomycete strains were isolated from soil samples, among which isolate no. 2 demonstrated  the strongest anti-MRSA activity. Molecular analysis revealed a 1205 bp 16S rRNA gene sequence showing 100% identity to  Streptomyces mutabilis. Phylogenetic analysis using the neighbor-joining method confirmed its close clustering with S. mutabilis  strain PQ668646 with maximal bootstrap support. Bioactive metabolites extracted from S. mutabilis exhibited potent antibacterial activity across MRSA isolates, with a minimum inhibitory concentration (MIC) of 10.0 µg/mL and a minimum bactericidal concentration (MBC) of 20.0 µg/mL. Significant antibiofilm inhibition was observed (p < 0.0001), highlighting their potential to prevent biofilm- associated device infections. Cytotoxicity assays against PC-3 prostate cancer cells indicated additional anticancer activity (IC50 +73.4±0.19 µg/mL). GC–MS profiling identified 30 metabolites, dominated by 9-octadecenamide (Z-), 1-docosene, and 9-hexacosene. HPLC confirmed 12 phenolic and flavonoid compounds, with syringic, ellagic, ferulic acid, and quercetin as major constituents. Collectively, these findings position Streptomyces mutabilis metabolites as promising candidates for developing novel antimicrobial and antibiofilm therapeutics against MRSA.