Staphylococcus aureus is known for its ability to tolerate high salt concentrations. Under which two of the following NaCl concentrations would S. aureus most likely survive?

• A. 0.5% and 15% NaCl
• B. 7.5% and 15% NaCl
• C. 0.5% and 7.5% NaCl
• D. 0.5% and 20% NaCl

Answer: (C)

Verified step by step guidance

1. Understand that Staphylococcus aureus is a halotolerant bacterium, meaning it can survive in environments with higher salt concentrations than many other bacteria.
2. Recognize that typical bacterial growth occurs at low salt concentrations (around 0.5%), but S. aureus can tolerate and grow in moderately high salt concentrations, such as 7.5%, which is commonly used in selective media like Mannitol Salt Agar.
3. Note that extremely high salt concentrations, such as 15% or 20%, are usually inhibitory or lethal to most bacteria, including S. aureus, because they cause osmotic stress that the bacteria cannot overcome.
4. Compare the given options and identify which pairs include salt concentrations within the tolerable range for S. aureus, focusing on 0.5% (low salt) and 7.5% (moderate high salt) as the most likely to support survival.
5. Conclude that the pair 0.5% and 7.5% NaCl represents the conditions under which S. aureus would most likely survive, based on its halotolerant nature and known growth characteristics.