Validation of the Peel Plate Staphylococcus Aureus (SA) Test for Enumeration of S. aureus in Selected Foods and Non-Cultured Dairy Products: AOAC Performance Tested MethodSM 082401.

Abstract

Background: The microbial testing platform, Peel Plate™, was developed with Baird Parker ingredients for Staphylococcus aureus (SA) specificity. After rehydrating with 1 mL of the diluted food sample, Peel Plate SA is incubated for 24-48 h at 35-37°C and observed for purple colonies.

Objective: A validation study was performed to evaluate Peel Plate SA for enumeration of SA in selected foods and non-cultured dairy products for Performance Tested MethodSM (PTM) certification.

Methods: Peel Plate SA was evaluated in inclusivity/exclusivity and matrix studies, product consistency and stability studies, and robustness testing. Non-fat dried milk, frozen raw cod fish, corned beef, frozen raw vegetables, potato salad, vegetable soup, frozen unshelled raw shrimp, and baby food (apple, cinnamon, and granola) were evaluated in the matrix studies comparing Peel Plate SA to US and international reference methods. Three levels of contamination along with non-inoculated controls were tested for each matrix.

Results: Peel Plate SA detected 49 of 50 SA isolates tested. Of the 38 exclusivity species tested, none were detected. In the matrix studies, the Peel Plate SA results were determined to be equivalent to the reference method results by paired statistical analysis. In an accelerated stability study, the shelf-life of Peel Plate SA was shown to be stable for 12 months. Equivalence was demonstrated between different production lots. Small changes to critical test parameters did not significantly affect the Peel Plate SA results.

Conclusion: Peel Plate SA is a ready-to-use method for enumeration of SA in a variety of foods and non-cultured dairy products. As with reference methods, Peel Plate SA colonies should be isolated and confirmed with differentiation tests such as catalase and strong coagulase positive.

Highlights: The data were reviewed by the PTM Program and certification was granted for the Peel Plate SA method PTM 082401.