Staphylococcus pseudintermedius as an Emerging Coagulase-positive Infection in Humans

To the Editor S taphylococcus pseudintermedius is a coagulase-positive staphylococci within the S. intermedius group, which also includes S. intermedius and Staphylococcus delphini. Because of biochemical similarities, S. pseudintermedius is commonly misidentified as Staphylococcus aureus. It is a leading cause of canine infections and is emerging as a zoonotic pathogen for humans. Matrix-assisted laser desorption/ionization-time of flight has improved identification of this organism with a specificity of 97%, possibly contributing to an increase in proper identification. The largest report identified 24 human cases; 75%were superficial infections, whereas 2 had invasive disease including a prosthetic joint infection (PJI) and 1 bacteremia.Most patients (92%) reported contact with dogs. Morganella morganii is a Gram-negative bacillus belonging to the Morganellaceae family within the Enterobacterales order. M. morganii is part of normal colonic microbiota and not typically associated with bone and joint infections. Thus, we present our experience with a PJI caused by S. pseudintermedius and M. morganii. A 54-year-old man first presented with drainage from surgical site wound incision after a left total knee replacement 3 weeks prior. The patient reported that he first noticed the drainage 4 days prior, which continued to bemore voluminous and associated with progressive swelling, intermittent fever and chills. On examination, the knee showed moderate swelling with copious amount of foul-smelling, bloody, and purulent drainage. There was preserved passive and active range of motion. The patient was taken for irrigation and debridement of left total knee arthroplasty with polyethylene exchange by the orthopedic team. Gram stains of the intraoperative cultures demonstrated Gram-positive cocci and Gram-negative bacilli. Initial blood work demonstrated an inflammatory response with C-reactive protein of 152.7 mg/L and erythrocyte sedimentation rate of 48 mm/h. Blood culture remained negative for 5 days. However, intraoperative tissue cultures grew S. pseudintermedius and M. morganii, identified by matrix-assisted laser desorption/ ionization-time of flight. Susceptibilities were determined using Vitek-2. Staphylococcus pseudintermedius was notably sensitive to clindamycin, daptomycin, doxycycline, levofloxacin, oxacillin, rifampin, and vancomycin.Morganella morganii showed only intrinsic resistance. A peripherally inserted central catheter (PICC) was placed, and the patient was discharged to receive 6 weeks of vancomycin, ceftriaxone, and rifampin. Two weeks later, the patient returned because of fever of 103°F, difficulty infusing vancomycin, and right upper arm pain. The PICC line was removed and sent for culture. Antibiotics were empirically changed meropenem, anidulafungin, and daptomycin for possible PICC line-related infection. Duplex venous ultrasound was positive for deep vein thrombosis involving right brachial and axillary veins; apixaban was initiated. Subsequently, the patient developed a rash after meropenem. Anidulafungin and meropenem were discontinued based on negative blood cultures. Ceftriaxone was restarted. A rash developed after ceftriaxone infusion leading to its discontinuation. The rash continued to worsen after daptomycin. After holding all antibiotics, the rash resolved. The patient started oral