A Rare Case of Post-sternotomy Mediastinitis Caused by Methicillin-Resistant Staphylococcus pseudintermedius, a Canine Commensal, Following Ascending Aortic Replacement.

Post-sternotomy mediastinitis (PSM) is one of the most serious infectious complications following cardiac surgery. It requires prompt diagnosis and comprehensive treatment, including antimicrobial therapy, surgical intervention, and wound management. In recent years, vacuum-assisted closure (VAC) therapy has become a widely accepted strategy for effective infection control and wound healing. It also serves as a valuable bridging therapy before definitive reconstruction, when needed. We report a rare case of PSM caused by methicillin-resistant (MRSP), a coagulase-positive Staphylococcus commonly found on dog skin. A 75-year-old man underwent ascending aortic replacement for a thoracic aortic aneurysm and developed fever and wound inflammation on postoperative day 11. Blood and wound cultures confirmed the presence of MRSP. Notably, the patient had no direct contact with the pet dog during hospitalization, suggesting that preoperative skin colonization was a likely source of infection. The patient underwent debridement, intravenous antibiotics, and VAC therapy. Infection control and wound healing were achieved without flap reconstruction, and the patient was discharged uneventfully. PSM caused by MRSP is extremely rare, and this case highlights the potential role of zoonotic pathogens in postoperative infections. The findings emphasize the importance of including pet ownership history in preoperative assessments and incorporating it into perioperative infection control planning. Awareness of rare but clinically relevant pathogens, such as MRSP, is essential for the effective management of surgical site infections.