Characterization and therapeutic potential of two Kayvirus phages against methicillin-resistant S. aureus in a rat myositis model.

PURPOSE: Methicillin-resistant Staphylococcus aureus (MRSA) continues to compromise the efficacy of conventional antibiotics, highlighting the urgent need for alternative antimicrobial strategies. This study aimed to isolate, characterize, and evaluate the therapeutic potential of two strictly lytic bacteriophages, Staphylococcus phages EAS1 and EAS2, against MRSA, including their safety and efficacy in an in vivo myositis model.

METHODS

EAS1 and EAS2 were isolated from wastewater and characterized using transmission electron microscopy, whole-genome sequencing, and in vitro functional assays. Genomic and comparative analyses were performed to assess genome organization and safety-related features. Therapeutic efficacy and toxicity were evaluated in a rat model of MRSA-induced myositis, with assessment of inflammatory mediators and histopathological tissue damage.

RESULTS

Both phages exhibited broad and potent lytic activity against S. aureus, including MRSA strains, and demonstrated high physicochemical stability and biocompatibility. Both phages possessed large linear dsDNA genomes (∼138-140 kb) encoding over 240 CDSs without lysogeny, virulence, or antibiotic resistance genes and were classified within the Kayvirus genus based on comparative genomics. In vivo, phage treatment caused no detectable hepatic or renal toxicity. EAS2 treatment led to significant modulation of inflammatory mediators, including TNF-α, IL-10, NF-κB, and COX-2, and resulted in reduced histopathological tissue damage compared with untreated control and vancomycin-treated groups.

CONCLUSION

These findings demonstrate the stability, safety, and therapeutic efficacy of bacteriophages EAS1 and EAS2, particularly EAS2, supporting phage therapy as a promising alternative approach for the treatment of MRSA infections.