A 29-year-old patient with acquired immunodeficiency syndrome (AIDS) is suspected of having a C. neoformans infection in the cerebrospinal fluid (CSF). A CSF specimen is collected and set up on cycloheximide agar. In addition, an India ink stain is set up. The India ink stain reveals encapsulated yeast; however, 3 weeks later, the cycloheximide agar is negative. Which one of the following
statements explains this discrepancy?
a. The India ink result is most likely false positive.
b. The ingredients in the cycloheximide agar most likely inhibited the growth of the organism.
c. C. neoformans is rarely recovered from CSF; therefore the cycloheximide result is accurate.
d. The India ink stain is most likely conta-minated.
B
Cycloheximide may be added to any of the media that contain or lack antibacterial antibiotics. However, if cycloheximide is included in the battery of culture media, then a medium lacking this ingredient should also be included. Pathogenic fungi, such as C. neoformans, Candida krusei, other Candida spp., Trichosporon cutaneum, Pseudallescheria boydii, and Aspergillus spp., are partially or completely inhibited by cycloheximide.
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