Validation of the CompactDry "Nissui" BC for Enumeration of Bacillus cereus in a Variety of Foods: AOAC Performance Tested MethodSM 092201.

Abstract

Background: The CompactDry "Nissui" BC is a ready-to-use dry media sheet using a chromogenic medium with selective agents for the detection and enumeration of Bacillus cereus in products after incubation at 30 ± 1°C for 24 ± 2 h.

Objective: The CompactDry "Nissui" BC method was validated to achieve AOAC Performance Tested MethodsSM certification.

Method: The performance of the CompactDry "Nissui" BC was compared to that of ISO 7932:2004 for 10 matrixes, including panna cotta, double cream, dried baby food, dried vegetable soup mix, seafood sticks, salmon pâté, sliced ham, pork liver pâté, ham and cheese sandwich, and Caesar pasta salad with chicken and bacon. Performance indicators included repeatability, difference of means (DOM), and inclusivity/exclusivity.

Results: After log10 transformation of the data, the relative standard deviation of repeatability (RSDr) was ≤9.2% for 28 of the 30 materials (10 matrixes each at three contamination levels) analyzed by the CompactDry "Nissui" BC method and ≤13% for 27 of the 30 matrix/level combinations analyzed by the reference method. Method equivalence was demonstrated in 28 of the 30 matrix/level combinations based on the 90% confidence interval of the DOM being within (-0.5, 0.5). For inclusivity, 47 of 50 strains tested showed typical colonies and confirmed positive. For exclusivity, 28 of 33 strains tested resulted in no growth or were negative, and five were positive. Inclusivity and exclusivity results were similar on the reference method agar. The method was shown to be robust to changes in sample volume, incubation temperature, and incubation time, and data are presented supporting product consistency and 18-month shelf life.

Conclusions: The CompactDry "Nissui" BC method is validated for the determination of Bacillus cereus in a variety of matrixes.

Highlights: The CompactDry "Nissui" BC method is equivalent to the ISO 7932:2004 reference method and is suitable for Performance Tested MethodsSM certification for the matrixes tested.