**Question:** All of the following statements about Staphylococcus aureus are true, except -

A. Staphylococcus aureus is a Gram-positive cocci bacteria commonly found in the skin and nasal passages of healthy individuals.
B. It is responsible for causing pneumonia, meningitis, and sepsis.
C. Staphylococcus epidermidis is a major cause of bloodstream infections in healthcare settings.
D. Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of community-acquired infections.

**Correct Answer:**

A. **Staphylococcus aureus is a Gram-positive cocci bacteria commonly found in the skin and nasal passages of healthy individuals.**

Staphylococcus aureus is indeed a Gram-positive cocci bacteria that can be found on the skin and nasal passages of many healthy individuals as a part of the normal skin flora. However, statement A is incorrect because it specifically mentions that Staphylococcus aureus is commonly found in the skin and nasal passages. In reality, this bacteria can be found in various body sites, not just these two.

**Why the Correct Answer is Right:**

Staphylococcus aureus is a ubiquitous bacterium that can inhabit various body sites, not just the skin and nasal passages. It is a significant pathogen that can cause a wide range of infections, including skin, soft tissue, bone, joint, respiratory, urinary, and bloodstream infections.

**Why Each Wrong Option is Incorrect:**

B. **Staphylococcus aureus is responsible for causing pneumonia, meningitis, and sepsis.**

While Staphylococcus aureus can cause pneumonia, meningitis, and sepsis, the correct answer is option A because it focuses only on the presence of the bacterium in the skin and nasal passages.

C. **Staphylococcus epidermidis is a major cause of bloodstream infections in healthcare settings.**

Staphylococcus epidermidis is a coagulase-negative staphylococcus and is often considered a commensal bacterium, meaning it is a part of the normal flora. While it is true that S. epidermidis can cause infections, especially in healthcare settings, the correct answer is option A because it specifically mentions S. epidermidis, not Staphylococcus aureus.

D. **Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of community-acquired infections.**

This statement is correct, as methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a significant cause of community-acquired infections, particularly in the context of antibiotic resistance. MRSA is resistant to multiple antibiotic classes, including penicillins and cephalosporins, which is why it is important to identify the correct bacteria causing an infection and ensure appropriate antibiotic therapy.

**Why the Correct Answer is Right:**

The correct answer is option A because it focuses on the presence of the bacterium in the skin and nasal passages, while options B, C, and D refer to specific strains and infections caused by Staphylococcus aureus, which