Hypertonic xylose agar medium: A novel medium for differentiation of Candida dubliniensis from Candida albicans

Candida dubliniensis fungemia in a patient with severe COVID-19: A case report

Candida dubliniensis phenotypically mimics Candida albicans in its microbiological features; thus, its clinical characteristics have yet to be fully elucidated. Here we report the case of a 68-year-old Japanese man who developed C. dubliniensis fungemia during treatment for severe coronavirus disease 2019 (COVID-19). The patient was intubated and received a combination of immunosuppressants, including high-dose methylprednisolone and two doses of tocilizumab, as well as remdesivir, intravenous heparin, and ceftriaxone. A blood culture on admission day 11 revealed Candida species, which was confirmed as C. dubliniensis by mass spectrometry. An additional sequencing analysis of the 26S rDNA and ITS regions confirmed that the organism was 100% identical to the reference strain of C. dubliniensis (ATCC MYA-646). Considering the simultaneous isolation of C. dubliniensis from a sputum sample, the lower respiratory tract could be an entry point for candidemia. Although treatment with micafungin successfully eradicated the C. dubliniensis fungemia, the patient died of COVID-19 progression. In this case, aggressive immunosuppressive therapy could have caused the C. dubliniensis fungemia. Due to insufficient clinical reports on C. dubliniensis infection based on definitive diagnosis, the whole picture of the cryptic organism is still unknown. Further accumulation of clinical and microbiological data of the pathogen is needed to elucidate their clinical significance.

Evaluation of various phenotypic methods for differentiation of Candida dubliniensis from Candida albicans

INTRODUCTION

Candida dubliniensis was first identified by Sullivan et al. (1995) in Dublin, Ireland. Its clinical significance is associated with development of fluconazole-resistance and invasive diseases in immunocompromised hosts. C. dubliniensis share many features with C. albicans so has been overlooked and misidentified for a long time.

AIMS

Evaluation of various phenotypic tests with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) as a gold standard to find out the best method/methods for identifying C. dubliniensis.

MATERIALS AND METHODS

First PCR-RFLP was performed on 186C. albicans and 14C. dubliniensis strains and then five phenotypic tests were performed simultaneously on all the strains.

RESULTS

The results of salt tolerance test at 48 h, colony color on HiCrome candida differential agar (HCDA) at 72 h, heat tolerance test at 48 h, xylose assimilation using discs at 72 h and growth on xylose based agar medium (XAM) at 48 h are completely concordant with PCR-RFLP. Colony color on Tobacco agar could differentiate accurately 100% test strains while peripheral hyphal fringes and chlamydosporulation on this agar was seen in only 86% and 87% respectively. Our routine methods proved to be cost effective than PCR-RFLP but the turnaround time was same or more than PCR-RFLP.

CONCLUSION

For routine identification of C. dubliniensis we recommend use of colony color on HCDA and growth on XAM as simple, reliable and inexpensive method.