In Vitro Activity of Bacteriophages Against Ocular Methicillin-resistant S. aureus Isolates Collected in the US.

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of sight-threatening infections in the US. These strains pose a significant challenge in managing ocular infections, as they frequently exhibit resistance to first-line empirical antibiotics. To assess the potential of bacteriophages as innovative topical therapies for treatment of recalcitrant ocular infections, we evaluated the in vitro antimicrobial activity of a set of anti-S. aureus phages against a collection of ocular MRSA clinical isolates collected in the US.

Methods: The host range of six phages (V4SA2, V1SA9, V1SA12, V1SA19, V1SA20 and V1SA22) was assessed using the spot assay on a panel of 50 multidrug-resistant (MDR) ocular MRSA isolates selected to be representative of clones circulating in the US. Subsequently, liquid culture-based host range assay was performed for the three most active phages using different multiplicity of infection (MOI of 10, 1 or 100 phages/bacteria).

Results: In total, 90.0% of bacterial isolates were susceptible to at least one of the six phages. The spot host range assay showed that phages V1SA19, V1SA20 and V1SA22 had the broadest spectrum, being active against 86%, 84% and 82% of the isolates, respectively, including the MDR-MRSA CC5 and the community-associated CC8 lineages. A phage dose effect was observed across the liquid culture-based host range assay.

Conclusion: Phages V1SA19, V1SA20 and V1SA22 exhibited high antimicrobial activity against ocular MRSA. Bacteriophages represent a promising anti-infective strategy in ophthalmology that could be explored for improved topical therapy of recalcitrant MRSA infections.