An image analysis system: an objective and accurate alternative for reading the agar diffusion test

Area of Science:

• Veterinary Diagnostics
• Microbiology
• Analytical Chemistry

Background:

• The agar diffusion test is a common microbiological assay.
• Manual interpretation of inhibition zones can be subjective and time-consuming.
• Accurate quantification of antimicrobial agents is crucial in veterinary diagnostics.

Purpose of the Study:

• To develop and validate an automated image analysis system (IAS) for reading agar diffusion tests.
• To assess the accuracy and precision of the IAS compared to manual methods.
• To evaluate the IAS for screening oxytetracycline in porcine plasma and urine samples.

Main Methods:

• Development of a computerized image analysis system (IAS) for automated zone of inhibition measurement.
• Screening of 88 porcine plasma and 95 urine samples for oxytetracycline using the agar diffusion test.
• Comparison of IAS measurements (direct and from photo-negative) with manual measurements.

Main Results:

• High positive correlation between IAS and manual methods for both plasma (r=0.9716, 0.9669) and urine (r=0.9878, 0.9731) samples.
• IAS demonstrated significantly lower coefficient of variation and day-to-day variation compared to manual methods.
• The IAS method proved accurate and precise within the tested range of 0.1 to 2.0 µg/ml.

Conclusions:

• The automated image analysis system (IAS) provides an objective and accurate alternative for reading agar diffusion tests.
• IAS offers improved precision and reduced variability in zone of inhibition measurements.
• This automated method is suitable for routine screening of antimicrobial agents like oxytetracycline in biological samples.