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Bacillus stearothermophilus disk assay for detection of residual penicillins in milk: collaborative study
Abstract:
A collaborative study was performed on a Bacillus stearothermophilus paper disk method designed to detect residual levels of 4 antibiotic drugs in whole market milk. This method is a modification of an earlier procedure developed for the International Dairy Federation. Whole milk samples spiked at low levels with ampicillin, cephapirin, cloxacillin, and penicillin G were sent frozen to 11 collaborating laboratories with instructions to assay them promptly according to the method provided. Five of the laboratories reported inconclusive results due to technical difficulties encountered with the method. The 6 remaining laboratories all detected levels of 0.005-0.008 microgram or unit/mL for penicillin G, ampicillin, and cephapirin and 0.05-0.08 microgram/mL for cloxacillin. The most commonly used official methods, the Sarcina lutea (Micrococcus luteus) cylinder plate method and the Bacillus subtilis paper disk method, can detect levels of 0.01 and 0.05 unit penicillin G/mL, respectively. The B. stearothermophilus method is rapid, simple to perform, and more sensitive than present official methods. The method has been adopted as official first action for the detection of penicillins in milk.
Insights
A new Bacillus stearothermophilus paper disk method offers a rapid and sensitive way to detect residual antibiotics like penicillin G in milk. This improved method is more effective than current official procedures.
Area of Science:
- Microbiology
- Food Safety
- Analytical Chemistry
Background:
- Antibiotic residues in milk pose a food safety concern.
- Existing detection methods have limitations in sensitivity and speed.
Purpose of the Study:
- To evaluate a modified Bacillus stearothermophilus paper disk method for detecting four antibiotic drugs in whole milk.
- To compare the sensitivity and efficiency of this method against established official procedures.
Main Methods:
- A collaborative study involving 11 laboratories.
- Whole milk samples were spiked with ampicillin, cephapirin, cloxacillin, and penicillin G.
- Samples were analyzed using the Bacillus stearothermophilus paper disk method.
Main Results:
- Six laboratories successfully detected antibiotic residues.
- The method detected penicillin G, ampicillin, and cephapirin at 0.005-0.008 µg/mL and cloxacillin at 0.05-0.08 µg/mL.
- This method demonstrated higher sensitivity compared to Sarcina lutea and Bacillus subtilis methods.
Conclusions:
- The Bacillus stearothermophilus method is rapid, simple, and more sensitive for detecting penicillins in milk.
- The method has been adopted as an official first action method for penicillin detection in milk.