GLORIA

Inclusion Criteria: 1. Male or female ≥ 18 years 2. Knee or Hip PJI according to EBJIS (European Bone and Joint Infection) or ICM (International Consensus Meeting) guidelines 3. Monobacterial Infection due to S. aureus 4. Without preoperative diagnosis of superinfection due to another pathogen if treatment is administered at the end of the DAIR (presence of a contaminant is not considered clinically relevant) 5. Without diagnosis of superinfection due to another pathogen identified within 72h after bacteriological sample performed during the DAIR if treatment is administered up to 14 days after the DAIR 6. Indication for Open DAIR decided by the Multidisciplinary Team and/or Principal Investigator 7. S. aureus in joint fluid during the pre-inclusion period or in case of relapse of infection under antibiotics therapy in the last 6 months before inclusion 8. Patient with a life expectancy of 1 year or more as determined by the principal investigator. 9. Females of childbearing potential/Sexually active males with partner of childbearing potential: commitment to consistently and correctly use an acceptable effective method of birth control until 1 month after the last study drug administration. 10. Females of non-childbearing potential: either surgically sterilized or at least 1 year postmenopausal (amenorrhea duration at least 12 months) Exclusion Criteria: 1. Relapse between DAIR and study drug administration planned up to 14 days after the DAIR. 2. Patients who have two planned DAIR in sequence (double DAIR) 3. Patients with ASA score ≥ 4 4. Severe sepsis or Septic shock or hemodynamic instability 5. Patients with an indication for fixed prosthesis exchange, or for joint fusion or for amputation 6. Indication for suppressive antibiotherapy 7. Immunosuppressed patients: Patients having a weakened immune system due to diseases conditions (i.e. genetic disorders, malnutrition) or treatment (i.e. anticancer drugs or organ transplant) 8. Positive Human Immunodeficiency Viruses (HIV) test or active hepatitis B and C 9. Previous treatment by bacteriophages 10. Any known phage allergy and/or to its excipients 11. Elevated ALT or AST above 4 times ULN