Combating Clinically Isolated Pathogens with Surfactin from a Newly Isolated Bacillus subtilis ZCK-1: from Strain Characterization to Therapeutic Potential

The escalating threat of multidrug-resistant (MDR) pathogens necessitates urgent exploration of natural antimicrobial alternatives. This study identified a novel surfactin-producing Bacillus subtilis strain ZCK-1 isolated from environmental soil. Whole-genome sequencing revealed a 4 043 370 bp (GC content: 43.73%) encoding 4041 protein-coding genes, including biosynthetic gene clusters for lipopeptides. A surfactin extract was obtained through XAD 16N macroporous resin adsorption coupled with ethanol elution and vacuum rotary evaporation. The surfactin demonstrated potent antibacterial activity against clinically critical Gram-positive pathogens, notably Streptococcus pneumoniae, Corynebacterium striatum, and drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). Mechanistic studies revealed dual modes of action: disrupting bacterial membrane integrity and degrading genomic DNA. The compound exhibited remarkable thermal stability (100°C, 30 min) and tolerance to extreme pH (2.0–13.0), proteases (trypsin/pepsin), while remaining susceptible to lipase-mediated degradation. Acute oral toxicity assays in murine models confirmed biosafety (LD50 > 5000 mg/kg). These findings position surfactin from B. subtilis ZCK-1 as a promising candidate for combating MDR infections in clinical and industrial settings.