Which yeast enzyme is detected using birdseed (niger seed) agar?

The correct answer is phenol oxidase. This enzyme is associated with certain types of fungi and yeasts, particularly those in the genus Cryptococcus. Birdseed agar, which contains niger seeds, is specifically formulated to identify Cryptococcus neoformans and similar organisms due to its ability to allow the expression of phenol oxidase.

When yeasts that possess this enzyme grow on birdseed agar, they produce pigments that give the medium a dark brown or black color. This biochemical reaction is crucial for identifying pathogenic yeasts, as it indicates the presence of phenol oxidase. The presence of this enzyme is a key diagnostic criterion in clinical microbiology for distinguishing Cryptococcus species, especially when examining samples from patients with infections.

The other enzymes listed do not have the same specific association with birdseed agar. Catalase is generally tested using hydrogen peroxide to observe bubbling, but it is not detected through birdseed agar. Urease is identified through the use of special media that change color in response to ammonia production, which does not occur on this medium. Nitrate reductase is assessed through different biochemical tests that measure the reduction of nitrate to nitrite or nitrogen gas, unrelated to the pigmentation seen on birdseed agar. Therefore, phenol oxidase