A novel phage endolysin inactivates a wide range of Staphylococcus aureus and eliminates mono- and mixed-species biofilms associated with S. aureus

Abstract Staphylococcus aureus and its single or mixed biofilm infections seriously threaten global public health. Phage therapy, which uses active particles or phage-derived endolysins, has emerged as a promising alternative strategy to antibiotic treatment. However, high-efficient phage therapeutic regimens have yet to be established. In this study, we used a mixed-sample procedure to isolate phages against methicillin-resistant S. aureus (MRSA) XN108. We characterized a new phage, SYL, sequenced its genomes, and engineered its novel endolysin, LysSYL. LysSYL demonstrated stability under various conditions and exhibited a broader range of efficacy against staphylococcal strains than its parent phage (100% vs. 41.7%). Moreover, dynamic live/dead bacterial observation demonstrated that LysSYL could completely inactivate MRSA USA300 within 10 min. Scan and transmission electron microscopy revealed evident bacterial cell perforation and deformation. In addition, LysSYL displayed strong eradication activity against single- and mixed-species biofilms associated with S. aureus . It also had the ability to disrupt bacterial persisters, and it proved highly effective in eliminating persistent S. aureus when combined with vancomycin. Furthermore, LysSYL protected BALB/c mice from lethal S. aureus infections. A single-dose treatment with 50 mg/kg of LysSYL resulted in a dramatic reduction in bacterial loads in the blood, liver, spleen, lungs, and kidneys of a peritonitis mouse model, which resulted in rescuing 100% of mice challenged with 10 8 colony forming units of S. aureus USA300. Overall, the data provided in this study highlight the strong therapeutic potential of endolysin LysSYL in combating staphylococcal infections, including mono- and mixed-species biofilms related to S. aureus .