An isolate from CSF growing on cornmeal agar produces specific structures. Which test should be performed next?

The isolate from cerebrospinal fluid (CSF) that grows on cornmeal agar and produces specific structures suggests that it may be a species of fungi, particularly considering that cornmeal agar is often used for identifying fungi due to its nutrient content that encourages the growth of certain yeast and molds.

When it comes to fungi, especially species like Cryptococcus neoformans, which is known to produce a capsule and can be tested using India ink to observe this characteristic, the subsequent test options provide insights into various identification techniques. However, the specific follow-up tests should be tailored to narrow down the identification further.

The choice of birdseed agar and urease is particularly relevant for identifying Cryptococcus neoformans. This fungus can grow on birdseed agar, which provides nutrients that allow for the demonstration of urease activity, resulting in a positive urease test. The ability to grow on birdseed agar and the urease test are both significant indicators that can help confirm the presence of this organism.

Other tests, such as the germ tube test, are more specific for yeasts like Candida albicans, while the India ink test typically provides visual confirmation of the capsule but does not specifically differentiate species. Hence, focusing on the combination of bird