Differentiation of Candida dubliniensis on chrom agar and Pal's agar.

ABSTRACT

Difference in expression of putative virulence factors and in antifungal susceptibility among different Candida species has raised the need for species-level identification. The close relationship of Candida dubliniensis with C. albicans has led to misidentification of C. dubliniensis isolates as C. albicans. Phenotypic tests include ability to produce chlamydospore on casein agar, colony colour development on differential media CHROM agar Candida medium and ability to form hyphal fringe on Pal's agar, have been used to differentiate these two Candida species. Fifty isolates of Candida species were recovered from various specimens (blood, urine, tissue and respiratory secretions) from diabetic and cancer patients between April and July 2007. The isolates were tested for chlamydospore production on casein agar. These were also streaked simultaneously on CHROM agar, Pal's agar and a combination of CHROM agar supplemented with Pal's agar for identification and differentiation of C. dubliniensis from C. albicans. On CHROM agar, 19 isolates were identified as C. dubliniensis, nine as C. albicans, 10 as C. krusei, nine as C. tropicalis and two as C. glabrata. One was indeterminate and later identified as C. dubliniensis. Out of the 20 C. dubliniensis isolates, 19 isolates exhibited hyphal fringe on Pal's agar. On CHROM agar supplemented with Pal's agar, 16 out of the 19 fringe-positive isolates exhibited fringe surrounding the bluish green-coloured colonies of C. dubliniensis. Additional identification tests like growth at 45 degrees C and ability to reduce 2,3,5-triphenyltetrazolium chloride were time efficient, inexpensive and easy-to-use methods for differentiation of C. dubliniensis and C. albicans isolates. CHROM agar when supplemented with Pal's agar gave definitive identification between C. dubliniensis and C. albicans.