Characterization and host range associating factors of Staphylococcus aureus bacteriophage PBSA08; Using Australian...

Antimicrobial resistance is a global health problem, with methicillin-resistant Staphylococcus aureus (MRSA) causing significant morbidity and mortality. As antibiotic options dwindle, (bacterio) phage therapy is re-emerging as a promising alternative.

We characterised a novel lytic S. aureus phage, PBSA08, and evaluated its host range using a reference panel of 39 MRSA isolates selected from the 2021 Australian Group on Antimicrobial Resistance repository. Phage susceptibility was tested by efficiency of plating (EOP) and growth kinetics assays (GKA). Factors associated with phage susceptibility were evaluated.

Phage PBSA08, classified under the genus Silviavirus, revealed an icosahedral head and long tail structure using transmission electron microscopy. Adsorption assays indicated efficient bacterial binding, with a burst size of approximately 120 plaque forming units (PFU) per infected cell. EOP testing revealed 51.3% of the MRSA reference panel isolates were susceptible (EOP ≥10%). GKA results correlated strongly with EOP. In univariate analysis, phage PBSA08 susceptibility was associated with multilocus sequence type (ST), ciprofloxacin susceptibility, and the presence of the Panton-Valentine leucocidin-associated genes, with all ST30-IV and ST93-IV isolates susceptible to PBSA08 and all ST45-V isolates resistant to PBSA08. Firth logistic regression showed that ST30/93 isolates had significantly higher odds of susceptibility (aOR 68.9, 95% CI 2.0-2378.5; P = 0.0191), as did ciprofloxacin-susceptible strains (aOR 15.4, 95% CI 1.7-143.0; P = 0.0160).

PBSA08 demonstrates potential as a therapeutic phage, particularly against community-associated MRSA lineages such as ST93. Its inclusion in phage cocktails targeting prevalent MRSA clones warrants further investigation.