Which characteristic best identifies Staphylococcus aureus in routine testing?

Which characteristic best identifies Staphylococcus aureus in routine testing?

• A. DNase negative
• B. Coagulase negative
• C. Growth inhibition in presence of increased salt
• D. Mannitol fermentation positive

Answer: (D)

The trait most useful for identifying Staphylococcus aureus in routine testing is its ability to ferment mannitol on mannitol salt agar. This medium is selective for staphylococci due to its high salt content, and it differentiates organisms by mannitol fermentation. Staph. aureus ferments mannitol, producing acid that lowers the pH and changes the indicator to yellow, often yielding yellow colonies with a yellow halo. This rapid color change on a standard, commonly used medium makes it a practical, reliable differentiator in everyday labs. The other options don’t fit as identifying features: DNase negative would contradict the typical DNase-positive nature of S. aureus, coagulase negative would contradict its commonly coagulase-positive status, and growth inhibition in high salt goes against the salt-tolerant, robust growth of Staphylococcus species.

The trait most useful for identifying Staphylococcus aureus in routine testing is its ability to ferment mannitol on mannitol salt agar. This medium is selective for staphylococci due to its high salt content, and it differentiates organisms by mannitol fermentation. Staph. aureus ferments mannitol, producing acid that lowers the pH and changes the indicator to yellow, often yielding yellow colonies with a yellow halo. This rapid color change on a standard, commonly used medium makes it a practical, reliable differentiator in everyday labs.

The other options don’t fit as identifying features: DNase negative would contradict the typical DNase-positive nature of S. aureus, coagulase negative would contradict its commonly coagulase-positive status, and growth inhibition in high salt goes against the salt-tolerant, robust growth of Staphylococcus species.