[The phenoloxidase test and its application to identify Cryptococcus neoformans with various biological...

Cryptococcus neoformans strains with various biological characteristics were examinated the phenoloxidase activity on the caffeic acid cornmeal agar (CACA). Other medically important yeasts were also included in this research. Firstly, thirteen reference strains of Cryptococcus neoformans were confirmly found positive phenoloxidase production on the CACA medium. Then, in total 150 isolates of yeasts, forty three Cryptococcus neoformans strains were phenoloxidase positive, other than that 107 other yeast strains were all negative. It is suggested that Cryptococcus neoformans strains with different biological features specifically and uniquely produce phenoloxidase, thus the phenoloxidase test can be applied as a useful tool to identify this pathogenic yeast. Our results also show that the culture on the CACA medium is an effective method to test the phenoloxidase activity within 72 hours. It is further approved that the urease test will not be able to be a screening test for Cryptococcus neoformans in the clinical laboratory, but it is still valuable to identify urease negative Cryptococcus neoformans when the test is used in combination with the phenoloxidase test.