Clinical laboratory evaluation of a screening medium (CN screen) for Cryptococcus neoformans

Results obtained with 433 yeast isolates indicated that the CN screen medium could be used with confidence for presumptive identification of Cryptococcus neoformans. Of 49 C. neoformans isolates tested, only four stock isolates yielded false-negative results upon initial testing. After repeated subculturing on Sabouraud agar and retesting, these four isolates yielded correct results. Essentially, no false-positive results were obtained, and the data suggested that false-negative results could be eliminated by using fresh isolates of C. neoformans preincubated at 25 degrees C on Sabouraud glucose agar.