Who publishes interpretive breakpoints used in AST and how often are they updated?

• A. FDA in the US, updated annually.
• B. CLSI in the US and EUCAST in Europe; updates typically annually or as issued.
• C. WHO updates quarterly.
• D. CDC updates every five years.

Answer: (B)

Interpreting antimicrobial susceptibility tests relies on threshold values that separate isolates into susceptible, intermediate, or resistant categories, based on MICs or zone diameters. The bodies that publish these interpretive breakpoints are CLSI in the United States and EUCAST in Europe. They continuously review data on drug pharmacodynamics, resistance mechanisms, and clinical outcomes, and issue updated breakpoints in regular guideline revisions. Updates typically occur annually or as new data warrant changes. Other organizations may guide labeling or surveillance, but the primary, routinely used interpretive criteria come from CLSI and EUCAST, making them the best answer.