Seven closely related isolates of Candida albicans exhibited progressive decreases in susceptibility to posaconazole. Sequencing of the gene involved in azole resistance in these strains revealed predicted proteins with single amino acid changes. Which of the following best describes the type of mutation that has resulted in decreased susceptibility to posaconazole in these strains?

**Core Concept**
The underlying principle being tested is the mechanism of antifungal resistance, specifically the development of resistance to azole antifungals like posaconazole in *Candida albicans*. This involves understanding how genetic mutations can alter the target of azole antifungals, leading to decreased susceptibility.

**Why the Correct Answer is Right**
The correct answer is related to the type of mutation that affects the target enzyme of azole antifungals, which is the lanosterol 14α-demethylase, encoded by the *ERG11* gene in *Candida albicans*. Mutations in this gene can lead to changes in the protein structure, reducing the binding affinity of azole antifungals and thus conferring resistance. Single amino acid changes can significantly impact the function of the enzyme.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not directly relate to the specific mechanism of azole resistance mediated by alterations in the target enzyme.
**Option B:** Similarly, this option is incorrect as it does not accurately describe the genetic basis of resistance in this context.
**Option C:** This choice is also incorrect because, while mutations are involved, the description does not accurately capture the nature of the mutations leading to azole resistance.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that mutations in the *ERG11* gene, leading to single amino acid changes in the lanosterol 14α-demethylase enzyme, are a common mechanism of resistance to azole antifungals in *Candida albicans*. This highlights the importance of monitoring antifungal susceptibility patterns, especially in patients with recurrent infections.

**Correct Answer:** D. Missense mutation.

✓ Correct Answer: B. Inversion