The rise of antibiotic-resistant bacteria, particularly methicillin-resistant Staphylococcus aureus (MRSA), poses a critical global health challenge. Endolysins, which enzymatically degrade bacterial cell walls, represent a promising class of antimicrobial agents. This study aimed to express and characterize the endolysin LysSW21, derived from the previously characterized Staphylococcus phage vBSauRSW21, and evaluate its antibacterial and antibiofilm activities against MRSA strains. In silico analysis of LysSW21 revealed a modular structure comprising an N-terminal CHAP catalytic domain (residues 20–107) and a C-terminal SH3b cell wall-binding domain (residues 164–228). The recombinant protein was successfully expressed in Escherichia coli BL21 (DE3) and purified. LysSW21 demonstrated potent bactericidal activity against reference MRSA strains (MIC/MBC: 25 μg/mL) and a clinical isolate from diabetic foot ulcer (MIC/MBC: 12. 5 μg/mL). Time-kill assays revealed rapid, concentration-dependent killing, with complete eradication of planktonic MRSA within 75 min at 2 × MIC (50 μg/mL) and within 105 min at MIC (25 μg/mL). The enzyme exhibited remarkable stability across a broad temperature range (4–70°C) and pH range (4. 5–10. 5), maintaining 4–5 log₁₀ reductions in bacterial viability. Importantly, crystal violet assay and field emission scanning electron microscopy confirmed concentration-dependent antibiofilm activity of LysSW21, with 70–80% biofilm disruption at 4 × MIC against MRSA strains. LysSW21 exhibits potent bactericidal activity against planktonic MRSA and effectively disrupts biofilms with high stability under diverse environmental conditions. These properties position LysSW21 as a promising candidate for further preclinical development against biofilm-associated MRSA infections. Future studies should evaluate its efficacy and safety in vivo.
Ranjbari et al. (Thu,) studied this question.