Distinguishing Candida species by beta-N-acetylhexosaminidase activity

A variety of fungi produce the hydrolytic enzyme beta -N-acetylhexosaminida se (HexNAcase), which can be readily detected in assays by using p-nitrophe nyl-N-acetyl-beta -D-glucosaminide as a substrate. In the present study we developed a microtiter plate-based HexNAcase assay for distinguishing Candi da albicans and Candida dubliniensis strains from other yeast species. HexN Acase activity was detected in 89 of 92 (97%) C. albicans strains and 4 of 4 C. dubliniensis strains but not in 28 strains of eight other Candida spec ies, 4 Saccharomyces cerevisiae strains, or 2 Cryptococcus neoformans strai ns. The HexNAcase activity in C. albicans and C. dubliniensis was strain sp ecific. All except three clinical C. albicans isolates among the C. albican s strains tested produced enzyme activity within 24 h. These strains did pr oduce enzyme activity, however, after a prolonged incubation period. For tw o of these atypical strains, genomic DNA at the C. albicans HEX1 gene locus , which encodes HexNAcase, showed nucleotide differences from the sequence of control strains. Among the other Candida species tested, only C. dublini ensis had a DNA sequence that hybridized with the HEX1 probe under low-stri ngency conditions. The microtiter plate-based assay used in the present stu dy for the detection of HexNA-case activity is a simple, relatively inexpen sive method useful for the presumptive identification of C. albicans and C. dubliniensis.