The E-test (epsilometer test) for antimicrobial susceptibility differs from disk diffusion primarily in that it:
- A Produces a continuous MIC value by reading the ellipse intersection with the strip ✓
- B Requires overnight broth microdilution to confirm results
- C Tests only one antibiotic concentration — the interpretive breakpoint
- D Uses agar dilution as the reference comparator for all readings
Correct answer: A. Produces a continuous MIC value by reading the ellipse intersection with the strip
Explanation
The E-test strip contains a predefined gradient of antibiotic concentrations, and when placed on an inoculated agar plate, a teardrop-shaped inhibition ellipse forms. The MIC is read where the ellipse intersects the strip's numerical scale, providing a quantitative MIC value directly from agar. This combines the simplicity of disk diffusion with the quantitative output of dilution methods. Disk diffusion only yields qualitative zone diameter categories (S/I/R), not an MIC.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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