Bacteriophage-Based Control of Methicillin-Resistant Staphylococcus aureus: Anti-Biofilm Activity, Surface-Active Formulation Compatibility, and Genomic Context

Background/Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) continues to pose a significant challenge for infection prevention, particularly because of its ability to persist on surfaces and form resilient biofilms. Although bacteriophages have attracted renewed interest as alternatives or complements to chemical disinfectants, their applied use requires careful assessment of antimicrobial performance, formulation tolerance, and genomic context. Methods: Staphylococcus-infecting bacteriophages were isolated from environmental sources and examined against reference Staphylococcus isolates. Two phage isolates, designated MRSA-W3 and SA-W2, displayed lytic activity against a broad subset of clinical MRSA strains. Using a time-resolved agar-based infection assay, phage exposure resulted in a multiplicity-of-infection-dependent decline in viable MRSA populations. Results: Time-resolved infection assays revealed a multiplicity-of-infection-dependent reduction in viable MRSA, with a pronounced decrease observed approximately 40 min post-infection. At this time point, phage-treated cultures showed a reduction of 1.2–1.8 log10 CFU/mL relative to untreated controls (mean Δlog10 = 1.5; 95% CI, 1.1–1.9), while control cultures remained stable. Quantitative biofilm assays demonstrated that both phages reduced biofilm biomass compared with untreated conditions, with inhibition values ranging from 20% to 45% across isolates (p ≤ 0.05), reflecting strain-dependent but reproducible effects. Assessment of formulation compatibility indicated that both phages retained infectivity following exposure to sodium dodecyl sulfate, Triton X-100, and Tween 80, whereas ethanol (≥10%) and higher concentrations of dimethyl sulfoxide were associated with rapid loss of activity. In surface disinfection models, selected phage–surfactant formulations achieved a maximum reduction of 2.18 log10 CFU/cm2 compared with untreated controls (p ≤ 0.05). Infection-coupled whole-genome sequencing of MRSA-infecting phage MRSA-W3 produced a high-quality assembly (99.99% completeness; 0.13% contamination) and revealed a mosaic genome containing incomplete prophage-like regions, which were interpreted conservatively as evidence of shared phage ancestry rather than active temperate behavior. Conclusions: Therefore, these findings suggest that bacteriophage-based approaches may be feasible for MRSA surface decontamination, while clearly emphasizing the need for context-specific validation before practical implementation.