In the context of antimicrobial susceptibility testing, when should zones of inhibition be measured?

• A. As soon as they are visible, regardless of their size
• B. After 72 hours of incubation, regardless of visibility
• C. Only if they are less than 10 mm in diameter
• D. Only after they exceed 25 mm in diameter

Answer: (A)

Verified step by step guidance

1. Understand that zones of inhibition in antimicrobial susceptibility testing represent areas where bacterial growth has been prevented by the antimicrobial agent.
2. Recognize that the timing of measuring these zones is critical because the size can change with incubation time and bacterial growth dynamics.
3. Recall that standard guidelines recommend measuring zones of inhibition as soon as they become visible to ensure accurate and consistent interpretation.
4. Note that waiting too long (e.g., 72 hours) or measuring only based on size thresholds (less than 10 mm or greater than 25 mm) can lead to inaccurate results or misinterpretation.
5. Therefore, the correct practice is to measure the zones of inhibition immediately once they are clearly visible, regardless of their size.