Hall, Laurence S.

ABSTRACTCryptococcus neoformansandCryptococcus gattiiare closely related pathogenic fungi.Cryptococcus neoformansis ecologically widespread and affects primarily immunocompromised patients, whileC. gattiiis traditionally found in tropical climates and has been reported to cause disease in immunocompetent patients.l-Canavanine glycine bromothymol blue (CGB) agar can be used to differentiateC. neoformansandC. gattii, but there are few reports of its performance in routine clinical practice. Growth ofC. gattiion CGB agar produces a blue color, indicating the assimilation of glycine, whileC. neoformansfails to cause a color change. Using reference and clinical strains, we evaluated the ability of CGB agar and D2 large ribosomal subunit DNA sequencing (D2 LSU) to differentiateC. neoformansandC. gattii.One hundred two yeast isolates were screened for urease activity, melanin production, and glycine assimilation on CGB agar as well as by D2 sequencing. Seventeen of 17 (100%)C. gattiiisolates were CGB positive, and 54 of 54C. neoformansisolates were CGB negative. Several yeast isolates other than theC. gattiiisolates were CGB agar positive, indicating that CGB agar cannot be used alone for identification ofC. gattii.D2 correctly identified and differentiated allC. gattiiandC. neoformansisolates. This study demonstrates that the use of CGB agar, in conjunction with urea hydrolysis and Niger seed agar, or D2 LSU sequencing can be reliably used in the clinical laboratory to distinguishC. gattiifromC. neoformans. We describe how CGB agar and D2 sequencing have been incorporated into the yeast identification algorithm in our laboratory.

ABSTRACT We evaluated aliquots from 244 clinical blood culture bottles that demonstrated yeasts on Gram stain using a Candida albicans peptide nucleic acid (PNA) fluorescent in situ hybridization (FISH) probe. The sensitivity, specificity, positive predictive value, and negative predictive value of the C. albicans PNA FISH test in this study were 99%, 100%, 100%, and 99.3%, respectively.