Study of the Activity of the Staphylococcus aureus Phage vB_SaS_GE1 Against MRSA Clinical Isolates and Its Impact on the Formation of Dual-Species Biofilms with P. aeruginosa

Bacteriophage therapy is regarded as a promising alternative for treating and preventing antibiotic-resistant bacterial infections. Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) is one of the most prevalent and difficult-to-treat pathogens. <i>S. aureus</i> also contributes to the formation of both single- and mixed-species biofilms. Treating biofilms remains a major challenge for antibiotic-based eradication of pathogens, as the biofilm matrix provides a protective barrier for bacteria. The selection of highly active phages targeting <i>S. aureus</i> is therefore crucial for medical applications, given the high prevalence and drug resistance of this pathogen. In this study, <i>S. aureus</i> phage vB_SaS_GE1 (GE1) was isolated and characterized as a potential therapeutic agent. The phage was isolated and propagated, and its host range was determined using standard methods. Whole-genome sequencing and annotation of the phage DNA were performed. A time-kill assay and evaluation of the anti-biofilm activity of the <i>Staphylococcus</i> phage, both alone and in combination with <i>Pseudomonas</i> phage GEC_PNG3 (PNG3) on mixed-species biofilms, were conducted. The results indicated that GE1 is a lytic phage that does not carry virulence-determining genes. The time-kill assay demonstrated sustained lytic activity of GE1 without the emergence of phage-resistant mutants in the tested MRSA strains. Although phage treatment increased biofilm matrix production compared to the control, the viable cell count within the biofilms was reduced. Overall, the characteristics assessed indicate that vB_SaS_GE1 is safe and exhibits strong antibacterial activity against MRSA strains.