A laboratory received a bronchioalveolar lavage specimen on a 74 year old male, who is now deceased. The potato flake agar grew white, mucoid colonies, while the Mycosel plate had no growth. The colony was identified as Cryptococcus neoformans by mass spectrometry.
Image 1. White mucoid colonies on potato flake agar.
C. neoformans and C. gattii produce white, mucoid colonies on a variety of agars that usually become visible within 48 hours. Urea and phenoloxidase are positive. L-Canavanine Glycine Bromothymol Blue (CGB) agar helps differentiate C. neoformans colonies from C. gattii, with C. neoformans producing a light green-blue color and C. gattii producing a cobalt blue color. C. neoformans is also described as resembling glass beads on cornmeal agar due the presence of its thick capsule. C. neoformans is generally 5-10 µm in size, however size is variable and they can be increased. Historically, India ink preparation was described to identify the organism due the capsule extruding the ink. Current identification methods include a rapid latex agglutination test for antigen, and mass spectrometry can also be used to identify C. neoformans.
C. neoformans and C. gattii are basidiomycetous, encapsulated yeasts found all over the world. They are commonly found in areas frequented by birds and bats. Patients with recent travel to caves or work in environments that expose them to chickens are at higher risk of infection due to inhalation of C. neoformans. While C. neoformans generally causes pulmonary infections, patients who are immunosuppressed can have disseminated cryptococcosis with CNS involvement. The clinical presentation of cryptococcosis due to the two species is generally indistinguishable. Cryptococcosis can be treated with amphotericin B and flucytosine or fluconazole.
-Mustafa Mohammad, MD is a 3rd year anatomic and clinical pathology resident at the University of Vermont Medical Center.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.