Which dimorphic fungus exhibits a filamentous mold form at room temperature and converts to yeast form above 35C?

The correct answer is Histoplasma capsulatum, a dimorphic fungus that exhibits two distinct forms depending on temperature. At room temperature, which is typically around 25°C, Histoplasma capsulatum exists in a filamentous mold form. This mycelial phase is characterized by its ability to reproduce through the formation of conidia.

As the temperature increases above 35°C, which occurs in the human body, the fungus transforms into a yeast form, which is more suited for survival in this warmer environment. This conversion from mold to yeast is a key feature of dimorphic fungi and in the case of Histoplasma capsulatum, this adaptation allows it to evade the host's immune response and establish infection.

Understanding the temperature-dependent phases of dimorphic fungi is crucial in microbiology, particularly when diagnosing infections caused by such organisms. For instance, other fungi listed do not follow this exact pattern: Candida albicans can exist primarily as yeast and also form pseudohyphae under certain conditions, Coccidioides immitis has a different temperature response, and Paracoccidioides brasiliensis also shows a dimorphic transition but has distinct characteristics in its temperature adaptability compared to Histoplasma capsulatum.