Which step in Kirby-Bauer is essential to ensure accurate diffusion?

Which step in Kirby-Bauer is essential to ensure accurate diffusion?

• A. Inoculate a lawn and observe colony morphology.
• B. Inoculate a lawn, place antibiotic-impregnated disks, incubate, measure zones of inhibition and compare to standard breakpoints.
• C. Streak for isolation and Gram stain.
• D. Use broth dilution instead.

Answer: (B)

Diffusion-based antibiotic testing relies on a defined antibiotic gradient created as the drug diffuses from a disk into a uniform bacterial layer. The essential step is to inoculate a uniform lawn, place antibiotic-impregnated disks, incubate under standardized conditions, then measure the zones of inhibition and compare the diameters to established standard breakpoints. This combination standardizes how diffusion is observed and how results are interpreted, ensuring the zone size truly reflects how the organism responds to the antibiotic. A uniform lawn ensures even diffusion and clear, circular zones; measuring the inhibition zones provides a quantitative readout; comparing to breakpoints standardizes interpretation across labs. Other actions, like watching colony morphology or Gram staining, focus on identification rather than diffusion patterns, and broth dilution uses a different approach to determine MIC rather than diffusion zones.

Diffusion-based antibiotic testing relies on a defined antibiotic gradient created as the drug diffuses from a disk into a uniform bacterial layer. The essential step is to inoculate a uniform lawn, place antibiotic-impregnated disks, incubate under standardized conditions, then measure the zones of inhibition and compare the diameters to established standard breakpoints. This combination standardizes how diffusion is observed and how results are interpreted, ensuring the zone size truly reflects how the organism responds to the antibiotic. A uniform lawn ensures even diffusion and clear, circular zones; measuring the inhibition zones provides a quantitative readout; comparing to breakpoints standardizes interpretation across labs. Other actions, like watching colony morphology or Gram staining, focus on identification rather than diffusion patterns, and broth dilution uses a different approach to determine MIC rather than diffusion zones.