Phage endolysin–polyphosphate/alginate nanocomplexes inhibit staphylococcal biofilms for implant protection

Implant-associated infections caused by Staphylococcus epidermidis and Staphylococcus aureus remain a major challenge in orthopedic surgery due to their robust biofilm formation and resistance to conventional antibiotics.We aimed to develop an alginate-based delivery system for peptidoglycan hydrolase–polyphosphate (PGH-PP) nanoparticles to prevent staphylococcal biofilm formation on implant surfaces. These nanoparticles incorporated two chimeric phage-derived endolysins, GH15 and M23. Formulations were screened for antimicrobial and antibiofilm activity against staphylococcal species using low- and very low-viscosity alginate. The nanostructure of the delivery systems was analyzed via transmission electron microscopy and phosphate release assays. Biocompatibility with MC3T3 preosteoblasts and the formulation´s impact on bone development were evaluated. Efficacy in inhibiting biofilm formation by S. epidermidis 9142 and S. aureus ATCC 25923 was assessed both on orthopedic implant surrogates and in co-culture experiments with MC3T3 preosteoblasts.Very low-viscosity alginate (0.625% w/v), in conjunction with a synergistic combination of M23-PP and GH15-PP, formed well-defined complex coacervates of approximately 350 nm (M23-PP/GH15-PP/VL alginate). The developed nanocomplexes effectively eradicated both bacterial species and further inhibited biofilm formation on implants, as confirmed by scanning electron microscopy. M23-PP/GH15-PP/VL alginate was biocompatible with MC3T3 preosteoblasts supporting its potential use in orthopedic applications. When MC3T3 cells were co-cultured with S. epidermidis or S. aureus, M23-PP/GH15-PP/VL alginate treatment led to an 8 log reduction in bacterial counts, with healthy mammalian cells proliferating in the absence of bacteria.These results highlight the potential of M23-PP/GH15-PP/VL alginate as a biocompatible approach to preventing staphylococcal biofilm formation, mitigating the risk of implant-related bone infections.