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

Abstract

Background: Candida dubliniensis is a pathogenic Candida species which shares many phenotypic features with Candida albicans. These similarities have caused significant problems in the identification of C. dubliniensis in an average clinical mycology laboratory. Several phenotypic-based tests have been developed to distinguish C. albicans from C. dubliniensis but none has been demonstrated being sufficient alone for accurate differentiation of the two species.

Aim: To facilitate the differentiation of these species, we evaluated the utility of a novel medium 'Hypertonic Xylose Agar Medium' (HXAM).

Materials and methods: A total of 200 Candida spp. were tested in this study which included 186 stock strains of C. albicans and 14 strains of C. dubliniensis. Identification of all these strains was confirmed by polymerase chain reaction-restriction fragment length polymorphism using Bln I (Avr II) enzyme. All isolates were inoculated on HXAM, incubated at 28°C and examined for visible growth every day up to 7 days.

Results: On this medium at 28°C, all 186 C. albicans isolates showed visible growth at 48 h of incubation whereas none of the 14 C. dubliniensis isolates did so even on extending the incubation period up to 7 days.

Conclusion: Hence, we propose HXAM as a sole phenotypic method for identifying C. dubliniensis from germ-tube-positive isolates or from stock collections of known C. albicans.