Which statement correctly differentiates qualitative AST reporting from quantitative MIC reporting?

Which statement correctly differentiates qualitative AST reporting from quantitative MIC reporting?

• A. Disk diffusion yields MIC values; E-test yields S/I/R with zone diameters; Breakpoints translate MIC to S/I/R.
• B. Disk diffusion yields qualitative S/I/R via zone diameters; E-test and broth microdilution yield MIC values; breakpoints translate MIC to S/I/R.
• C. Breakpoints translate zone diameters to S/I/R, and MIC methods are qualitative.
• D. E-test yields qualitative S/I/R; broth microdilution yields S/I/R; disk diffusion yields MIC.

Answer: (B)

In antimicrobial testing, the difference is between reporting categories (qualitative) and reporting exact numbers (quantitative). Disk diffusion doesn’t give a numeric MIC. It measures the zone of inhibition around a disk, and the size of that zone is interpreted using breakpoints to assign susceptible, intermediate, or resistant. In contrast, E-test and broth microdilution directly yield an MIC value—the lowest concentration that prevents growth. That MIC is then interpreted with breakpoints to determine S, I, or R. So the statement that disk diffusion provides qualitative categories via zone diameters, while E-test and broth microdilution provide MIC values, and breakpoints map MIC to S/I/R, correctly distinguishes qualitative reporting from MIC-based reporting.

In antimicrobial testing, the difference is between reporting categories (qualitative) and reporting exact numbers (quantitative). Disk diffusion doesn’t give a numeric MIC. It measures the zone of inhibition around a disk, and the size of that zone is interpreted using breakpoints to assign susceptible, intermediate, or resistant. In contrast, E-test and broth microdilution directly yield an MIC value—the lowest concentration that prevents growth. That MIC is then interpreted with breakpoints to determine S, I, or R. So the statement that disk diffusion provides qualitative categories via zone diameters, while E-test and broth microdilution provide MIC values, and breakpoints map MIC to S/I/R, correctly distinguishes qualitative reporting from MIC-based reporting.