Quantitative estimates of beta-lactam residues in raw milk around a reference standard: collaborative study

Area of Science:

• Microbiology
• Food safety analysis
• Analytical chemistry

Background:

• Accurate detection of penicillin in raw milk is crucial for food safety and preventing antibiotic resistance.
• Existing methods may lack the sensitivity or reliability required for regulatory standards.
• The Bacillus stearothermophilus disc assay is a potential candidate for sensitive penicillin detection.

Purpose of the Study:

• To assess the reliability and discriminatory power of the Bacillus stearothermophilus disc assay for quantifying penicillin in raw milk.
• To establish the minimum number of replicates required for statistically significant results.
• To support the official adoption of the method.

Main Methods:

• A collaborative study involving multiple laboratories.
• Testing of 10 raw milk samples (including a negative control) in blind duplicates.
• Use of triplicate standards alternated with triplicate unknown samples across 5 plates.
• Measurement of zone diameters and analysis using a paired t-test.

Main Results:

• The Bacillus stearothermophilus disc assay reliably distinguished penicillin concentrations differing by as little as 0.003 IU/mL.
• A 95% confidence level was achieved in differentiating penicillin concentrations.
• The assay demonstrated sufficient discriminatory power with as few as 3 plates (9 replicates) per unknown sample.

Conclusions:

• The Bacillus stearothermophilus disc assay is a reliable and sensitive method for differentiating penicillin concentrations in raw milk.
• The method's efficiency allows for accurate detection with a minimal number of replicates.
• The study's findings led to the official adoption of the method.