Which statement describes why some MIC methodologies are time-consuming and relegated to reference labs?

Which statement describes why some MIC methodologies are time-consuming and relegated to reference labs?

• A. Agar dilution
• B. Broth macrodilution
• C. Broth microdilution
• D. Disk diffusion

Answer: (A)

Agar dilution is time-consuming because it requires a separate agar plate for every drug concentration, and each plate must be inoculated and incubated independently. This creates a labor-intensive workflow with a large number of plates to prepare, handle, and read, which limits throughput and increases the potential for variability. The method also lacks the level of automation common with other MIC techniques, making it slower and more resource-intensive overall. Because of these factors, agar dilution is typically reserved for reference laboratories where precise MIC values are needed for unusual pathogens, validation, or special cases, rather than routine clinical testing. In contrast, broth microdilution tests many concentrations in microtiter plates, enabling higher throughput and easier automation, and disk diffusion provides rapid, simple results that categorize susceptibility without requiring exact MICs. Those factors keep them as the preferred options for daily testing in most clinical labs.

Agar dilution is time-consuming because it requires a separate agar plate for every drug concentration, and each plate must be inoculated and incubated independently. This creates a labor-intensive workflow with a large number of plates to prepare, handle, and read, which limits throughput and increases the potential for variability. The method also lacks the level of automation common with other MIC techniques, making it slower and more resource-intensive overall. Because of these factors, agar dilution is typically reserved for reference laboratories where precise MIC values are needed for unusual pathogens, validation, or special cases, rather than routine clinical testing.

In contrast, broth microdilution tests many concentrations in microtiter plates, enabling higher throughput and easier automation, and disk diffusion provides rapid, simple results that categorize susceptibility without requiring exact MICs. Those factors keep them as the preferred options for daily testing in most clinical labs.