Two novel Silviavirus phages with lytic activity against methicillin-resistant Staphylococcus aureus: genomic and phenotypic characterization

The increasing prevalence of multidrug-resistant (MDR) Staphylococcus aureus , particularly methicillin-resistant S. aureus (MRSA), necessitates alternative antimicrobial strategies. Here, we isolated and characterized two bacteriophages, CARØ0038 and CARØ0046, from sewage in Davangere, Karnataka, India, using MRSA as the host. Transmission electron microscopy revealed icosahedral heads with short tails, consistent with the class Caudoviricetes . Whole-genome sequencing identified genomes of 120,939 bp and 136,667 bp, with 227 and 225 predicted coding sequences and GC contents of 29.5% and 29.1%, respectively. Whole-genome phylogenomic and taxonomic analyses placed both phages within the genus Silviavirus and supported their distinction from closely related reference phages, although the available analyses did not establish definitive species-level assignment. Both phages exhibited efficient lytic activity against MRSA, with an MOI of 0.1 yielding the highest experimentally observed titres. One-step growth analysis demonstrated apparent latent periods of 15–20 min and burst sizes of 49 and 47 PFU/cell for CARØ0038 and CARØ0046, respectively. Both phages showed high infectivity up to 37 °C, with marked reductions at 45–50 °C and no detectable recovery at 60 °C. Maximum recovery occurred at pH 7, with no detectable infectious phage outside pH 6–8. Host-range analysis demonstrated clear lysis against all 28 MRSA isolates tested and activity against methicillin-susceptible S. aureus , while no detectable lysis was observed against S. epidermidis or S. saprophyticus under the conditions tested. No known antimicrobial resistance-associated or virulence-associated genes were identified. Collectively, these findings support CARØ0038 and CARØ0046 as distinct Silviavirus phages with efficient lytic activity against S. aureus , including MRSA, and provide a basis for further investigation of their potential as phage-based antimicrobial candidates.