Adjuvant multisite bacteriophage cocktail administration as salvage treatment in a patient with a multidrug-resistant Pseudomonas aeruginosa frontal relapsing complex osteitis

BACKGROUND: Bone infection due to multidrug-resistant (MDR) Pseudomonas aeruginosa is associated with poor outcomes, especially high risk of relapses. Adjunctive multisite phage therapy can be used as a salvage treatment in relapsing cases. CASE PRESENTATION: We treated a 37-year-old man with MDR P. aeruginosa frontal osteitis and a large frontal fistula, who experienced three relapses, using personalized multisite phage therapy combined with surgery and prolonged antibiotics (ceftolozane/tazobactam). The multisite phage administration included in situ instillation of the manufactured phage cocktail during surgery, followed by daily intravenous infusion and nebulization for seven days after surgery. No adverse events were reported during treatment. At the two-year follow-up, the patient had no relapse without any suppressive treatment. CONCLUSION: Multisite phage administration is a personalized treatment strategy that can prevent relapse or the emergence of additional antimicrobial resistance in complex cases, such as relapsing MDR P. aeruginosa osteitis.