Abstract
Aim
To investigate the ability of the bacteriophage Sb-1 to treat and prevent implant-associated infections due to methicillin-resistant Staphylococcus aureus (MRSA) in Galleria mellonella larvae implanted with a K-wire.
Method
The stability of Sb-1 in G. mellonella larvae was investigated by injecting a phage titer of 108 PFU and evaluating the presence of Sb-1 in hemolymph at different time points. For infection experiments, sterile stainless-steel K-wires (4 mm, 0.6 mm Ø) were implanted into larvae. Two days after implant, larvae were infected with MRSA ATCC 43300 (1×105 CFU) and incubated at 37°C for further 2 days. Implanted-infected larvae were thus treated for 2 days (3×/day) with 10µL of: i) PBS; ii) Sb-1 (107 PFU); iii) Daptomycin (4mg/kg), iv) PBS (24h)/Daptomycin(24h); v) Sb-1(24h)/Daptomycin(24h). To evaluate the prophylactic efficacy of Sb-1, an experiment based on phages or vancomycin (10mg/kg) administration, followed by MRSA infection of implanted larvae was performed. Both two days post-infection and post-treatment, K-wires were explanted, and the material was sonicated and plated for MRSA colony counting.
Results
Sb-1 titer resulted stable in hemolymph of G. mellonella larvae for 6–8 h post-administration. Two days post-infection of K-wire implanted larvae, ≈5×107 CFU/ml MRSA were found on the material. K-wires from larvae treated with Sb-1 or Daptomycin showed a MRSA CFU/ml reduction of ≈1 log compared to the CFU/ml values of the untreated control. The staggered administration Sb-1/Daptomycin determined higher CFU reduction (≈ 3.5 log). Prophylaxis with Sb-1 prevented MRSA infection of 7out of 10 larvae similarly to vancomycin.
Conclusions
G. mellonella larvae implanted with K-wires are a suitable model to test antibiofilm formulations in vivo. Sb-1 phage is able to prevent implant-associated infection due to MRSA in larvae. Sequential combination of Sb-1 and Daptomycin strongly reduces the MRSA load on implanted K-wires.
