What is the readout of an E-test on agar?

What is the readout of an E-test on agar?

• A. A drop-shaped inhibition ellipse
• B. A zone of inhibition diameter
• C. A turbidity measurement in broth
• D. A color change on plate

Answer: (A)

An E-test readout is the inhibition boundary around the gradient antibiotic strip. The strip releases a continuous range of concentrations into the agar, so bacteria are inhibited where the local concentration meets the organism’s MIC. This creates a curved, typically drop-shaped ellipse of inhibition that wraps around the strip. Reading the MIC is done at the point where this edge intersects the scale on the strip, which gives the MIC value in the strip’s units. This differs from disk diffusion (zone diameter), broth turbidity (broth tests), or color-change readouts.

An E-test readout is the inhibition boundary around the gradient antibiotic strip. The strip releases a continuous range of concentrations into the agar, so bacteria are inhibited where the local concentration meets the organism’s MIC. This creates a curved, typically drop-shaped ellipse of inhibition that wraps around the strip. Reading the MIC is done at the point where this edge intersects the scale on the strip, which gives the MIC value in the strip’s units. This differs from disk diffusion (zone diameter), broth turbidity (broth tests), or color-change readouts.