Isolation and characterization of bacteriophages active against methicillin-resistant Staphylococcus pseudintermedius.

We aimed to isolate and characterize bacteriophages (phages) with preferential activity against methicillin-resistant Staphylococcus pseudintermedius (MRSP), a multidrug-resistant canine pathogen. Four phages were isolated from canine faeces using two MRSP strains as initial hosts. Phage host range was evaluated by the spot test on 17 MRSP, 43 methicillin-susceptible S. pseudintermedius (MSSP), and six other staphylococci isolated from dogs. Transmission electron microscopy was used for presumptive identification followed by whole genome sequencing (WGS). All phages lysed all MRSP isolates whereas only 16-28% of MSSP were lysed. Their lytic activity was limited to S. pseudintermedius and S. schleiferi. All phages had similar morphology and belonged to the Siphoviridae family. WGS indicated that the phages were 93.8-99.7% identical to each other, and exhibited the highest similarity (87%) to the temperate S. aureus phage 187. Confirmatory lytic activity tests showed that phages were able to produce clear plaques on lysogens, which was enabled by recombination of the lysogeny modules as shown by WGS of the phages after propagation and plaque formation. This study provides insight into the genetic diversity and biology of S. pseudintermedius temperate phages, which could be further developed for topical therapy of MRSP skin and wound infections.

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