Disk diffusion results are interpreted by comparing observed zone diameters to what?

Disk diffusion results are interpreted by comparing observed zone diameters to what?

• A. Breakpoints established by CLSI or EUCAST.
• B. The color of the agar plate.
• C. The patient’s age.
• D. The lab's preferred chart.

Answer: (A)

Disk diffusion interpretation hinges on comparing the measured inhibition zone to standardized breakpoints published by CLSI or EUCAST. After incubation, you measure the zone diameter in millimeters and determine whether it falls into susceptible, intermediate, or resistant categories for that organism–antibiotic pair. These breakpoints are specific to each combination and reflect clinical pharmacology and resistance data, helping guide treatment decisions. The color of the agar plate, the patient’s age, or a lab’s personal chart don’t provide standardized thresholds for susceptibility, so they’re not used in interpretation.

Disk diffusion interpretation hinges on comparing the measured inhibition zone to standardized breakpoints published by CLSI or EUCAST. After incubation, you measure the zone diameter in millimeters and determine whether it falls into susceptible, intermediate, or resistant categories for that organism–antibiotic pair. These breakpoints are specific to each combination and reflect clinical pharmacology and resistance data, helping guide treatment decisions. The color of the agar plate, the patient’s age, or a lab’s personal chart don’t provide standardized thresholds for susceptibility, so they’re not used in interpretation.