Which of the following characteristics is most commonly associated with Staphylococcus aureus?

• A. Coagulase positivity
• B. Lack of catalase enzyme
• C. Gram-negative rod morphology
• D. Beta-hemolysis on MacConkey agar

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the general characteristics of Staphylococcus aureus. It is a Gram-positive bacterium, which means it retains the crystal violet stain and appears purple under a microscope.
2. Step 2: Recall that Staphylococcus aureus is catalase positive, meaning it produces the enzyme catalase that breaks down hydrogen peroxide into water and oxygen. Therefore, 'lack of catalase enzyme' is not a characteristic of S. aureus.
3. Step 3: Recognize that Staphylococcus aureus is coagulase positive. Coagulase is an enzyme that clots plasma, and this trait is commonly used to differentiate S. aureus from other Staphylococcus species.
4. Step 4: Note that Staphylococcus aureus is a coccus (spherical) bacterium, not a rod-shaped one, so 'Gram-negative rod morphology' does not apply.
5. Step 5: Understand that while S. aureus can exhibit beta-hemolysis on blood agar, MacConkey agar is selective for Gram-negative bacteria and does not support the growth of Gram-positive bacteria like S. aureus, so beta-hemolysis on MacConkey agar is not a relevant characteristic.