A rare case of Trichosporon inkin bloodstream infection in an immunocompetent patient: Diagnostic challenges and antigenic cross-reactivity

Trichosporon inkin is a rare opportunistic pathogen typically associated with superficial infections but can also cause invasive infections, particularly in immunocompromised hosts. Here, we report a rare case of T. inkin bloodstream infection in an immunocompetent male with a history of cerebral hemorrhage surgery. The patient presented with fever, limb twitching, and brain lesions. Blood cultures revealed fungal growth, which was initially misidentified as Trichosporon ovoides by mass spectrometry but was later confirmed as T. inkin through ITS and IGS1 sequencing. The isolate exhibited low MICs for azoles and amphotericin B but high MICs for echinocandins. Notably, the patient's serum tested positive for cryptococcal antigen and Aspergillus galactomannan, despite the absence of clinical signs of cryptococcosis or aspergillosis. The T. inkin isolate expresses cryptococcal antigen but not galactomannan cross-reactive antigens when cultured in standard media. However, it expresses galactomannan cross-reactive antigens when cultured in human whole blood. This case highlights diagnostic challenges, including antigenic cross-reactivity and misidentification, and emphasizes the role of host–pathogen interactions in antigen expression. Our findings underscore the need for improved diagnostics and cautious interpretation of fungal antigen tests. This report expands the understanding of T. inkin infections and provides insights into their clinical management. • A rare case of T. inkin bloodstream infection in an immunocompetent patient was reported. • Initial misidentification of T. inkin as T. ovoides by mass spectrometry highlights diagnostic limitations. • T. inkin cross-reacts with Aspergillus galactomannan, detectable only after stimulation in human whole blood.