AOAC-OMA/MicroVal Harmonized Validation of Peel PlateTM EB (Enterobacteriaceae Bacteria), First Action 2018.05

BACKGROUND Peel PlateTMEnterobacteriaceae Bacteria (EB) is dried selective media on a 47 mm plastic plate that produces enzyme substrate colored colonies on rehydration and incubation for 24 h and up to 48 h at 37 ± 1°C. PURPOSE The method validation compared quantification of EB to reference methods ISO 21528:2017 Parts 1 and 2. METHODS Matrixes compared were whole milk, skim powdered milk, vanilla ice cream, butter, infant formulas (soy- and dairy-based), infant cereals ± probiotic, environmental sponge swab of stainless steel surface, and poultry carcass rinse with two different peptone buffers. RESULTS In inclusivity and exclusivity studies, the method detected 54 of 54 EB strains and did not detect 30 of 30 non-EB strains. In matrix studies, the claimed foods were tested at three contamination levels using paired analysis between the reference and Peel Plate EB methods. Colony-forming units per gram or mL [CFU/g (mL)] were log10 transformed for statistical analysis. The candidate method and reference method were shown to be equivalent by the performance requirement of all 95% confidence intervals on mean difference falling between -0.5 and +0.5 log10 CFU/g (mL). An international collaborative study with dried infant formula spiked with Cronobacter sakazakii at log10 CFU/g (mL) 1.05, 2.31, and 3.21 levels, produced method differences -0.16, 0.15, and 0.18 log10 CFU/g (mL) with repeatabilities (r) = 0.33, 0.20, and 0.12 log10 CFU/g (mL) and reproducibilities (R) = 0.45, 0.26, and 0.18 log10 CFU/g (mL). CONCLUSIONS Based on these evaluations, the candidate method is considered equivalent to the reference methods at both the 24 h and 48 h incubation periods at 37 ± 1°C. HIGHLIGHTS Ready to use Enterobacteriaceae method equivalent to ISO-21528:2017 Parts 1 and 2; EB test colored colonies at 37°C for 24 h are equivalent at 48 h incubation; Singlet determined CFU/mL are statistically the same as duplicate average results; EB test validated for infant formula and dairy products including with probiotics; EB test for environmental surfaces and poultry carcass rinses using peptone buffers.