Which organism is commonly used as an example of a moderately hazardous agent suitable for BSL-2?

• A. Mycobacterium tuberculosis
• B. Escherichia coli K-12
• C. Staphylococcus aureus
• D. Ebola virus

Answer: (C)

Understanding biosafety levels and how organisms are categorized by risk is what this question tests. BSL-2 is designed for organisms that can cause human disease but are typically manageable with standard lab precautions plus protective gear and practices to prevent exposure and the spread of aerosols. These agents are considered moderate risk: infections are generally treatable, and healthy people often recover with appropriate care. Staphylococcus aureus fits this level well because it commonly causes skin infections, pneumonia, and bloodstream infections, yet it is routinely handled in teaching and clinical labs under BSL-2 conditions with proper PPE, containment practices, and hygiene.

In contrast, Mycobacterium tuberculosis requires BSL-3 due to its airborne transmission and higher virulence, and Ebola virus requires the highest containment at BSL-4 because of extreme risk and lethality. Escherichia coli K-12 is a nonpathogenic lab strain that is typically treated as BSL-1, presenting minimal risk under standard precautions. So Staphylococcus aureus is the classic example of a moderately hazardous organism appropriate for BSL-2.