**Question:** Mistuda reaction is read at:

A. 24 hours
B. 48 hours
C. 72 hours
D. 7 days

**Core Concept:** The Mistuna reaction is a culture technique used in mycology to differentiate between different species of fungi, particularly between Aspergillus and Penicillium species. It involves the growth of fungi on culture medium containing antibiotics or other growth inhibitors specific to certain fungi.

**Why the Correct Answer is Right:** The Mistuna reaction is read at 72 hours because this is the time point when the inhibition zones around the antibiotics become visible and allow for the differentiation between Aspergillus and Penicillium species. The reaction is based on the growth inhibition zones caused by the antibiotics in the medium, which differ in size and shape for each species.

**Why Each Wrong Option is Incorrect:**

A. 24 hours: This is too early for the inhibition zones to develop and allow for accurate differentiation between the fungi species.
B. 48 hours: The reaction is not fully visible or distinct at this time point, making the reading less reliable.
D. 7 days: The prolonged incubation period significantly increases the risk of contamination and may not accurately reflect the specific inhibition zones for Aspergillus and Penicillium species.

**Clinical Pearl / High-Yield Fact:** The Mistuna test is a valuable tool in mycology laboratories for differentiating between Aspergillus and Penicillium species, which is crucial for proper identification and treatment of mycoses caused by these organisms.

**Correct Answer:** C. 72 hours

The Mistuna reaction is read at 72 hours as this time point allows for the development of distinct inhibition zones that can differentiate between Aspergillus and Penicillium species. This test aids in the accurate identification of these fungi, which is essential for appropriate antifungal therapy and patient management in mycology laboratories.