Validation of PhageDx (TM) Cronobacter Assay for the Identification of Cronobacter Spp. in Powdered Infant Formula: AOAC Performance Tested Method(SM) 051803

Background: The PhageDx((TM))Cronobacter Assay is based on the infection of Cronobacter spp. by specific bacteriophages and expression of a luciferase reporter gene. Results are generated in as little as 18.5h for powdered infant formula (PIF). Objective: An AOAC Performance Tested Methods(SM) (PTM) study was conducted to validate the PhageDx Cronobacter Assay for the detection of Cronobacter in 10, 100, and 300 g milk- and soy-based PIF test portions. Method: The performance of the PhageDx method was compared to the ISO 22964:2006/2017 Microbiology of the Food Chain-Horizontal Method for the Detection of Cronobacter spp. and the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) Chapter 29 Cronobacter: 2012. Inclusivity/exclusivity, product consistency and stability, and robustness testing also were conducted. Results: There was no significant difference between the 10, 100, or 300g test portions for the milk and soy PIF matrixes between the PhageDx Cronobacter Assay, the ISO 22964:2006/2017, and the FDA BAM Chapter 29 Cronobacter: 2012 methods. The reporter bacteriophages were specific for Cronobacter and infected 75 strains in inclusivity testing. They did not infect 35 non-Cronobacter bacteria in exclusivity testing. Robustness testing showed that the method performed well with specific deviations from the standard protocol. Consistency and stability testing demonstrated that the recombinant phage gave consistent results across three production lots and was stable when stored under appropriate conditions for at least 3 months. Conclusions: Work in the submitting and independent laboratories demonstrated that the PhageDx Cronobacter Assay meets the qualifications for PTM status. Highlights: The PhageDx Cronobacter Assay is a rapid, simple, and specific test that has shown equivalence to both the FDA BAM and ISO reference methods for detecting Cronobacter spp. in PIF.