Bacillus stearothermophilus disc assay for detection of inhibitors in milk: collaborative study.
A 2-part (A and B) collaborative study was conducted on a Bacillus stearothermophilus paper disc (12.7 mm) method to detect residual inhibitors in milk. The 18 participating collaborators assayed raw milk samples spiked with a beta-lactam (penicillin G). Of the 18 collaborators, 14 participated in part A and 16 in part B. Part A demonstrated that either Antibiotic Medium No. 4 or PM Indicator Agar is suitable for use in the assay. The lowest concentration detectable, not significantly different from 100% at the alpha = 0.05 level, was 0.008 unit/mL with either medium. Part B demonstrated that the sensitivity of the method is equal to that of the current AOAC method (16.131-16.136). The concentration of beta-lactam detected by 50% of the analysts was 0.003-0.005 unit/mL in this study, compared with 0.005 unit/mL reported in an earlier collaborative study on the current AOAC method. No false positive results were reported in part A or part B. All samples found positive by the confirmatory test in part B were correctly identified as a beta-lactam with commercial Penase discs. The lowest concentration detectable by the method, not significantly different from 100% at the alpha = 0.05 level, was 0.008 unit/mL. The method was adopted official first action.
D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D001681:Biological Assay / Q000379:methods; D002417:Cattle; D001411:Geobacillus stearothermophilus / Q000187:drug effects / Q000254:growth & development; D008892:Milk / Q000032:analysis*; D010400:Penicillin G / Q000032:analysis
D000900:Anti-Bacterial Agents; D010400:Penicillin G