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

Abstract

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.

Keywords: BlnI (ArvII); C. albicans; C. dubliniensis; PCR-RFLP; Phenotypic identification; XAM; Xylose assimilation.