Which of the following is a pathogenic yeast?

Cryptococcus neoformans is classified as a pathogenic yeast because it is capable of causing infections in humans, particularly in immunocompromised individuals. This organism is known for causing cryptococcosis, which can manifest as pneumonia or meningitis. The ability of Cryptococcus neoformans to produce a thick capsule allows it to evade the immune system, making it particularly virulent.

In contrast, Penicillium chrysogenum is not a pathogenic yeast; it is primarily known for its role in antibiotic production, specifically penicillin. Bacillus subtilis is a bacterium, not a yeast, and is generally non-pathogenic, often found in soil and as a part of the normal gut flora in humans. Staphylococcus aureus is also a bacterium and is known for being pathogenic, but it is distinct from yeast, belonging instead to the category of bacteria. Thus, Cryptococcus neoformans stands out as the only option that fits the classification of a pathogenic yeast.