Distinguishing Candida Species by β-N-Acetylhexosaminidase Activity

ABSTRACT

A variety of fungi produce the hydrolytic enzyme β-N-acetylhexosaminidase (HexNAcase), which can be readily detected in assays by usingp-nitrophenyl-N-acetyl-β-d-glucosaminide as a substrate. In the present study we developed a microtiter plate-based HexNAcase assay for distinguishing Candida albicans and Candida dubliniensis strains from other yeast species. HexNAcase activity was detected in 89 of 92 (97%)C. albicans strains and 4 of 4 C. dubliniensisstrains but not in 28 strains of eight other Candidaspecies, 4 Saccharomyces cerevisiae strains, or 2Cryptococcus neoformans strains. The HexNAcase activity inC. albicans and C. dubliniensis was strain specific. All except three clinical C. albicans isolates among the C. albicans strains tested produced enzyme activity within 24 h. These strains did produce enzyme activity, however, after a prolonged incubation period. For two 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 Candidaspecies tested, only C. dubliniensis had a DNA sequence that hybridized with the HEX1 probe under low-stringency conditions. The microtiter plate-based assay used in the present study for the detection of HexNAcase activity is a simple, relatively inexpensive method useful for the presumptive identification ofC. albicans and C. dubliniensis.