First Report of Catheter-related Bloodstream Infection Caused by Filobasidium magnum

To the Editors: Filobasidium magnum (formerly Cryptococcus magnus) is an environmental, yeast-like fungus generally regarded as having low pathogenicity.1 However, it has been reported in rare infections, including chronic periprosthetic shoulder arthritis,2 vaginitis3 and nasal colonization in immunocompromised children.4 Here, we describe the first case of catheter-related bloodstream infection caused by F. magnum in a 19-year-old female with Hirschsprung disease. The patient, with a history of Hirschsprung disease requiring a colostomy and long-term central venous catheterization for parenteral nutrition, presented with fever, redness and swelling around the colostomy site. She was admitted with suspected catheter-related bloodstream infection and cellulitis, and empiric therapy with cefotaxime and teicoplanin was initiated. On day 2, a blood smear revealed yeast-like organisms (Figure, Supplemental Digital Content 1, https://links.lww.com/INF/F969), prompting the addition of micafungin. By day 3, the patient’s clinical status had not improved, leading to the addition of liposomal amphotericin B and ethanol lock therapy. The initial blood culture was negative for Gram-positive cocci, allowing for the discontinuation of teicoplanin. Following treatment with liposomal amphotericin B, the patient’s fever subsided. On day 6, subsequent blood cultures were negative, and micafungin was discontinued. The cellulitis resolved by day 7, allowing cefotaxime completion. Due to limited vascular access, a central venous catheter exchange at the same site was performed on day 20. The patient was discharged with a 2-week course of outpatient liposomal amphotericin B. She remained asymptomatic with no recurrence of the fungemia during 6 months of follow-up. The admission blood culture showed no growth in PF plus culture bottles (Biomérieux, Tokyo, Japan) at 35°C. The lack of growth prompted consideration of lipid-dependent Malassezia spp. A sample from the yeast-positive smear was directly inoculated onto potato dextrose agar with olive oil and tween 80 and a chromogenic agar plate specific for Malassezia spp. Colonies developed after 3 days of incubation at 30°C (Figure, Supplemental Digital Content 2, https://links.lww.com/INF/F969). Sequencing of the internal transcribed spacer region of the rRNA identified the organism as F. magnum, corresponding to IFM 69099 in the Medical Mycology Research Center database, Chiba University. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (Bruker Daltonics, Bremen, Germany) confirmed a close similarity to F. magnum strain CBS 4685, with a score of 1.81, consistent with genus-level identification. Antifungal susceptibility testing was conducted according to Clinical and Laboratory Standards Institute M27 guidelines5 (Table 1). Although F. magnum has no established breakpoints, testing indicated susceptibility to liposomal amphotericin B, while micafungin had a high minimum inhibitory concentration. TABLE 1. - The MIC Values of Filobasidium magnum Amphotericin B Fluconazole Itraconazole Voriconazole Posaconazole Flucytosine Caspofungin Anidulafungin Micafungin Khan et al4 0.75 8 1 0.125 0.5 >32 >32 >32 ND Khan et al4 0.75 24 4 0.19 1 >32 >32 >32 ND Ghajari et al3 0.062 0.062 0.031 ND ND ND ND ND ND Present case 1 16 0.25 0.25 ND >64 8 ND >16 ND indicates not done. This case represents the first documented catheter-related bloodstream infection due to F. magnum, underscoring the need to consider this pathogen in cases of yeast-positive blood smears with negative cultures. F. magnum exhibited slow growth at 25°C on potato dextrose agar with or without lipid and limitedly grew at 35°C, indicating its inclusion in the differential diagnosis of rare fungemia, particularly in immunocompromised or catheter-dependent patients. ACKNOWLEDGMENTS We thank James R. Valera for his assistance with editing this manuscript.