Characterization of Trichosporon spp. Isolates from Blood Stream And Central Nervous System Infections in A Tertiary Hospital in Singapore

Background:

The lack of accurate identification and susceptibility data on Trichosporon spp. limit our understanding and treatment of this emerging pathogen.

Methods:

We performed a retrospective review of blood stream (BS) or central nervous system (CNS) infections with Trichosporon spp.. Archived isolates were subcultured onto Sabouraud dextrose agar. Colonies were identified using bioMérieux API 20C AUX, Bruker MALDI-TOF Biotyper, sequencing of internal transcribed spacer (ITS) region and D1/D2 region of the 28S ribosomal subunit for correlation. Susceptibility testing was performed using Sensititire YeastOne Y010 broth dilution panel.

Results:

There were 14 cases of BS or CNS infections with archived isolates available for further characterization. Two T. inkin and 12 T. asahii isolates were identified by ITS and D1/D2 sequencing; which were concordant with MALDI-TOF. One T. asahii isolate was misidentified as T.inkin on API 20C AUX. All Trichosporon spp. have high MIC to echinocandins of >8mcg/ml. MIC ranges of T. asahii were: (a) fluconazole 2-8mcg/ml, (b) itraconazole 0.06-0.5mcg/ml, (c) voriconazole 0.015-0.25mcg/ml, and (d) posaconazole 0.12-0.5mcg/ml. The MIC₉₀ of T. asahii were (a) fluconazole 8.0mcg/ml, (b) itraconazole 0.25mcg/ml, (c) voriconazole 0.25mcg/ml, and (d) posaconazole 0.5mcg/ml. MIC ranges for T. inkin were (a) fluconazole 0.5-1mcg/ml, (b) itraconazole 0.12mcg/ml, (c) voriconazole 0.06mcg/ml, and (d) posaconazole 0.12mcg/ml. Applying CLSI breakpoints for Candida albicans, T. inkin were susceptible to both fluconazole and voriconazole; all except 1 T. asahii were resistant to fluconazole and demonstrated variable susceptibility to voriconazole. Most patients were critically ill in the intensive care unit and on ventilatory support (71.4%), with central lines (78.6%) and had underlying hematological malignancy (71.4%). Inpatient mortality rate was 78.6%.

Conclusion:

Identification of T. asahii and T. inkin by MALDI-TOF, ITS and D1/D2 sequencing appear to be concordant; discrepancies with API 20C AUX may occur. T. inkin has low MIC to the azoles; T. asahii susceptibility is more variable. Voriconazole appears to the drug of choice for T. asahii. Based on MIC values, fluconazole may be used for T. inkin.