Unmasking Candida viswanathii in Panel-Negative Candidemia Through Integrated MALDI-TOF MS and FTIR Spectroscopy

Background: Rare fungal infections may represent under-recognized causes of healthcare-associated sepsis, particularly when caused by emerging or difficult-to-identify pathogens. We aimed to characterize Candida viswanathii isolates recovered in the setting of panel-negative candidemia and to assess the contribution of an integrated diagnostic workflow. Methods: We investigated seven C. viswanathii isolates overall, including three recovered at our institution from blood, urine, and bronchoalveolar lavage of a NICU patient, as well as four bloodstream isolates from a second pediatric center included for comparison. Isolates were analyzed by culture and microscopy, three MALDI-TOF MS platforms, internal transcribed spacer sequencing, Fourier transform infrared (FTIR) spectroscopy and antifungal susceptibility testing. Results: C. viswanathii was repeatedly recovered from blood, urine and bronchoalveolar lavage, while the FilmArray BCID2 panel remained negative. All MALDI-TOF MS systems with updated databases correctly identified the yeast at the species level; identification was confirmed by sequencing. Fourier transform infrared analysis showed clustering of clinical isolates and clearly separated C. viswanathii from related Candida species. All isolates exhibited low MICs to echinocandins and amphotericin B as well as moderately elevated fluconazole MICs (2–4 mg/L). Conclusion: This study supports the use of explicit diagnostic algorithms for rare fungal pathogens in yeast-positive, syndromic panel-negative blood cultures. In this setting, updated MALDI-TOF MS libraries and FTIR spectroscopy may provide useful adjunctive support for the recognition and phenotypic discrimination of atypical yeasts within an integrated laboratory workflow.