Mediastinitis and Fungal Osteomyelitis Due to Trichoderma Longibrachiatum in a Heart Transplant Recipient: A Diagnostic and Therapeutic Challenge

Trichoderma longibrachiatum is a filamentous fungus found in soil. Although long considered a contaminant, its pathogenic role in humans has been increasingly described over recent decades, with reports of pulmonary, peritoneal, and endocardial infections, particularly in immunosuppressed patients. A 70-year-old man with heart failure underwent heart transplantation five months earlier and was receiving tacrolimus, mycophenolate, and prednisone. He presented with bulging and drainage from the sternal wound. Chest CT showed extensive osteolysis from the manubrium to the mid-sternal body and an abscess within muscle-adipose planes. Empiric therapy with piperacillin-tazobactam and vancomycin was started, and surgical removal of sternal wires with debridement was indicated. Direct microscopy of surgical material revealed mycelial filaments, prompting initiation of liposomal amphotericin B. Fungal culture of bone and mediastinal fragments identified Trichoderma longibrachiatum, confirming fungal mediastinitis with osteomyelitis, and voriconazole was added. No bacterial growth was detected, allowing antibiotics to be stopped after 16 days. The patient remained clinically stable, but with persistent low-volume drainage. After 30 days, amphotericin was discontinued and voriconazole was maintained as monotherapy. Fifteen days later, drainage increased again, requiring a new surgical approach, with repeat identification of the fungus. Minimum inhibitory concentration (MIC) testing suggested resistance to voriconazole (MIC 6 mg/L) and caspofungin (MIC 32 mg/L), but susceptibility to amphotericin B (MIC 1.0 mg/L). Voriconazole was discontinued and liposomal amphotericin B was reintroduced, planned for six weeks. The patient remains hospitalized with favorable clinical course and marked reduction in wound drainage. This case illustrates the pathogenic potential of Trichoderma longibrachiatum in immunosuppressed patients and highlights how advances in microbiological techniques enable its identification. Management is challenging due to the lack of standardized MIC breakpoints and reports of resistance to multiple antifungal classes. This is a rare report of fungal mediastinitis and sternal osteomyelitis late after heart transplantation, with failure of azole monotherapy and clinical response only to liposomal amphotericin B.