**Core Concept**
MRSA (Methicillin-resistant Staphylococcus aureus) is a type of bacterial infection caused by a strain of Staphylococcus aureus that has developed resistance to beta-lactam antibiotics, including methicillin. This resistance is primarily due to the presence of the mecA gene, which encodes for a modified penicillin-binding protein (PBP2a) that has a low affinity for beta-lactam antibiotics.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of MRSA resistance. MRSA is resistant to beta-lactam antibiotics, including methicillin, due to the mecA gene, which encodes for the modified PBP2a. This modified PBP2a has a low affinity for beta-lactam antibiotics, allowing the bacteria to continue to grow and multiply despite the presence of these antibiotics. The mecA gene is responsible for the beta-lactam resistance in MRSA.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because MRSA is not resistant to all antibiotics; in fact, it is resistant to a specific class of antibiotics, beta-lactam antibiotics.
**Option B:** This option is incorrect because MRSA is not caused by the mecA gene alone; it is the result of a combination of genetic and environmental factors.
**Option C:** This option is incorrect because MRSA is not a type of viral infection; it is a bacterial infection caused by Staphylococcus aureus.

**Clinical Pearl / High-Yield Fact**
MRSA is a type of bacterial infection that requires specific treatment with antibiotics that are not affected by the mecA gene, such as vancomycin or daptomycin.

**Correct Answer: C. MRSA is a type of bacterial infection caused by Staphylococcus aureus, not a viral infection.**