Characterization, genomic analysis and preclinical evaluation of the lytic Staphylococcus bacteriophage PSK against methicillin-resistant Staphylococcus aureus wound isolate.

Abstract

Background: The dissemination of multi-drug-resistant bacteria, particularly Methicillin-resistant Staphylococcus aureus (MRSA), necessitates exploring new alternatives for their control. Bacteriophages are promising antibiotic alternatives with unique features. Here, we have performed a comprehensive characterization of a newly isolated bacteriophage (PSK) and compared its therapeutic potential with vancomycin in vivo.

Methods: Sewage samples were processed and enriched with the MRSA S. aureus SK1 strain in a search for isolation of a lytic bacteriophage. The isolated bacteriophage was assessed in vitro in terms of thermal and pH stability and kinetic parameters using absorption and one step growth curve assays. Moreover, its potential antibacterial activity was evaluated against S. aureus SK1 lone and in combination of standard of care antibiotics used for treatment of wound infections. We further analyzed its genome to exclude the presence of any potential toxin or antibiotic resistance genes. Finally, its antibacterial potential and capability to alleviate wound infection were assessed using a murine wound-infection model.

Results: The lytic bacteriophage (PSK) was isolated as a new species of the genus Rosenblumvirus with a genome size of 17,571 bp that is free from potential resistance or virulence genes. PSK displays infectivity against 4/10 S. aureus strains including two vancomycin-resistant strains. Moreover, it demonstrates favorable infection kinetics of fast adsorption with latent period and burst size of 20 min and 123 PFU/infected cell, respectively. Stability analysis revealed thermal stability up to 60 °C with wide pH range stability (4-11). In vitro, PSK kills S. aureus SK1 with multiplicity of infection (MOI) as low as 10^- 4 with an overall mutation frequency of 2.47 × 10^- 6 CFU/mL that is further improved when combined with 0.25× MIC of oxacillin, fusidic acid or vancomycin. In vivo, a single dose of PSK in murine wound infection model exhibited a comparable performance to four doses of vancomycin, when treatment started 2 h post-infection. However, when applied 2 days post-infection, PSK demonstrates superior antibacterial activity (up to 4.58 log unit count reduction) and enhances wound closure and tissue healing.

Conclusion: These findings represent PSK as a potential vancomycin alternative effective in treating S. aureus- induced wound infections.