To the Editor: We have read with interest numerous studies investigating the clinical role of daptomycin, particularly in invasive infections with hypothesized biofilm formation as an important pathogenic mechanism of infection.1 This is true for Propionibacterium acnes, a commensal microbe with an opportunistic ability to cause serious central nervous system, endovascular, and orthopedic infections. Given its ability to treat biofilm-forming infections, particularly in the setting of indwelling prosthetic material, as well as its convenient once-daily dosing, daptomycin is an attractive option for treatment of serious infections due to P. acnes. Previously, Ghosh et al2 and Taylor et al3 have published a case report of P. acnes osteomyelitis of the skull treated with daptomycin. P. acnes septic arthritis in native joints and postoperatively after shoulder surgery has been reported.3,4 Here, we report a case of P. acnes septic arthritis of the left shoulder treated with daptomycin. A middle-aged man with a history of well-controlled diabetes (hemoglobin A1c 6.3%) presented to our hospital with a 1-week history of low-grade fevers and left shoulder pain with movement. He underwent arthroscopic rotator cuff repair of the same shoulder 3 weeks before hospital presentation. Arthrocentesis was performed for synovial fluid analysis, revealing 104,000 white blood cells/mm3 with 92% polymorphonuclear cells. Gram stain showed no organisms. The C-reactive protein was 237 mg/L, and the erythrocyte sedimentation rate was 115 mm/h. Serum white blood cell count was 12,500 cells/mm3 with 72% polymorphonuclear cells. The patient was started on empiric daptomycin dosed at 6 mg/kg intravenous daily and proceeded for operative drainage and washout of the shoulder on first hospital day. On hospital day 5, initial synovial fluid culture showed that P. acnes evolved under anaerobic conditions. Subsequent surgical cultures on repeat surgical washouts were sterile. The patient was continued on daptomycin on hospital discharge and completed 6 weeks of therapy. After completion of therapy, the erythrocyte sedimentation rate was 17 mm/h and the result from the C-reactive protein test was negative. He regained full range of motion shortly after hospitalization and remained well without recurrence thereafter. P. acnes is a facultative gram-positive anaerobic bacillus. Shoulder infections due to P. acnes have become an emerging problem. P. acnes was the most commonly reported organism in a recent meta-analysis of shoulder periprosthetic joint infections, representing 38.9% of infections.5 Risk factors included increased age, male sex, increased body mass index, and diabetes mellitus. Antibiotic management is not clearly defined. Penicillin G, amoxicillin plus rifampin (RIF), clindamycin plus RIF, and linezolid plus RIF have been used.4 Clinicians must be aware that microbiological diagnosis can be difficult because anaerobic conditions and prolonged duration are necessary for culture. Clinicians should also be aware of the high incidence of P. acnes infection after shoulder surgery. Our case illustrates the utility of daptomycin as a convenient and promising treatment for serious P. acnes orthopedic infections. Rahul Mahapatra, DO Stony Brook University Hospital Stony Brook, NYGeorge Psevdos, MD Veterans Affairs Medical Center Northport, NY Stony Brook University School of Medicine Stony Brook, NY [email protected]