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 7 days after surgery. No adverse events were reported during treatment. At the 2-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.