Which organizations may disagree on breakpoints for antimicrobial susceptibility testing?

• A. CLSI and EMA
• B. FDA and CLSI
• C. NIH and FDA
• D. WHO and CLSI

Answer: (B)

Breakpoints are the interpretive thresholds used to decide if a microbe is susceptible, intermediate, or resistant to a drug based on MICs or zone sizes. They come from different organizations that serve distinct roles. The FDA sets breakpoints tied to how a drug is labeled—its approved dosing, indications, and the clinical data used for approval. CLSI, on the other hand, provides consensus interpretive criteria for routine laboratory testing, drawing on broader PK/PD data, surveillance, and clinical outcomes across many settings. Because these sources rely on different data and purposes, their breakpoints can diverge. In practical terms, a MIC might be deemed susceptible under CLSI criteria but not under FDA labeling, or vice versa. That’s why FDA and CLSI are the pairs most likely to disagree on breakpoints.