Which organism is described as appearing black on Gram-stain preparations?

Which organism is described as appearing black on Gram-stain preparations?

• A. Aspergillus
• B. Dematiaceous Fungi
• C. Candida albicans
• D. Cryptococcus neoformans

Answer: (C)

Pigmentation in certain fungi comes from melanin in their cell walls, giving a dark brown-to-black appearance under microscopy. Fungi with this pigment are called dematiaceous and they often look black on Gram-stain preparations because the pigment is visible alongside the stain. Candida albicans is a nonpigmented yeast that typically appears as Gram-positive purple budding cells (and sometimes pseudohyphae); it does not have the dark pigmentation that produces a black appearance. Aspergillus is a pale, or hyaline, mold and would not look black. Cryptococcus neoformans has a capsule and stains variably on Gram stain; its characteristic feature isn’t a black pigment. So, the description of appearing black on Gram-stain preparations points to dematiaceous fungi rather than Candida albicans.

Pigmentation in certain fungi comes from melanin in their cell walls, giving a dark brown-to-black appearance under microscopy. Fungi with this pigment are called dematiaceous and they often look black on Gram-stain preparations because the pigment is visible alongside the stain.

Candida albicans is a nonpigmented yeast that typically appears as Gram-positive purple budding cells (and sometimes pseudohyphae); it does not have the dark pigmentation that produces a black appearance. Aspergillus is a pale, or hyaline, mold and would not look black. Cryptococcus neoformans has a capsule and stains variably on Gram stain; its characteristic feature isn’t a black pigment.

So, the description of appearing black on Gram-stain preparations points to dematiaceous fungi rather than Candida albicans.