Precision Parameters for AOAC Bacillus stearothermophilus Disc Assay Based on FDA Milk Laboratory Quality Assurance 1982-1986 Samples.

Inhibitory substance (antibiotic) test results from State Split Milk Samples were used to estimate precision parameters and to compare antibiotic medium 4 (A4) and PM indicator (PM) agars. Five inhibitory substances (ampicillin, cephapirin, erythromycin, neomycin, and penicillin-G) were tested. Repeatability relative standard deviations (RSDr) ranged from 1.0 to 4.8%, and the reproducibility relative standard deviations (RSDR) ranged from 4.8 to 10.4%. Zone sizes of erythromycin, neomycin, and penicillin-G were significantly larger on PM agar (α = 0.05) than on A4 agar. The reverse was observed for cephapirin. No difference between agars was noted for ampicillin.

Detectability and Precision of the AOAC Bacillus stearothermophilus Disc Assay Demonstrated in the 1981 FDA Split Milk Sample Testing Program.

Four blind duplicate milk samples containing ß-lactam residues were analyzed by 149 analysts at 47 laboratories. Four official variations were used: (a) antibiotic 4 (A4) agar and 55°C incubation, (b) A4 agar and 64°C incubation, (c) PM indicator (PMI) agar and 55°C incubation, and (d) PMI agar and 64°C incubation. A ß-lactam concentration of 0.008 IU/ml was detectable 100% of the time by variations a, b, and c and 98% of the time by variation d, with average zone diameters of 18.7, 17.7, 16.4 and 17.6 mm, respectively. The 0.005 IU/ml concentration was detected 92% of the time by variation a, 99% by b, 57% by c and 89% by d, with average zone diameters of positive units of 16.3, 15.5, 14.9 and 15.2 mm, respectively.

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.

Variation in Food Microbiological Tests Used to Evaluate Analyst Performance.

Procedures for evaluating analyst performance in state and federal milk and food laboratory quality assurance programs depend on the estimates of variation for the methods used. The total components of variance for a method consist of replicate error, among-analysts variance, and analyst-sample interaction components. Eleven methods were evaluated in this study. Total variance estimates of milk analytical procedures for the Standard Plate Count, plate loop count, coliform plate count, direct microscopic somatic cell count, electronic somatic cell count and Wisconsin mastitis test were 0.01045, 0.01371, 0.01590, 0.01265, 0.00504 and 4.06, respectively. Estimates of the logarithmic total variance of food analytical procedures for the aerobic plate count, coliform most probable number (MPN), Escherichia coli MPN, fecal coliform MPN and Staphylococcus aureus MPN were 0.00853, 0.10205, 0.14705, 0.14780 and 0.24245, respectively. The study showed that current analyst performance levels used by state and federal laboratory quality assurance programs are satisfactory.

Incidence of Clostridium botulinum type E in Alaskan salmon.

The incidence of Clostridium botulinum type E in salmon captured in the coastal waters and rivers of Alaska during the 1968 commercial fishing season was determined.