Comparison of Rapid Detection Methods of Salmonella Enteritidis and E. coli O157:H7 in Cookie Dough

Introduction: Cookie dough is recognized as a potential vehicle for Salmonella for using egg as one of its ingredients. In 2009, commercial raw cookie dough was also reported as a novel vehicle for E. coli O157:H7 transition. Rapid detection methods for pathogens in cookie dough are in critical need to prevent foodborne outbreak and ensure food safety.

Purpose: The goal of this study is to compare rapid detection essays, including multiplex PCR and real-time PCR, to standard culture method for their sensitivity in detecting Salmonella and E. coli O157:H7 in cookie dough.

Methods: Samples of artificially inoculated cookie dough were incubated at 37°C for up to 24 hours. In culture method, Salmonella and E. coli O157:H7 were detected by selective plating on selective media. In multiplex PCR, invA and hilA genes were used to detect Salmonella; stx1, stx2, and rfbE gene were used to detect E. coli O157:H7. For real-time PCR, SureTect Pathogen Detection kit was used with PikoReal real-time PCR system for both pathogens. While various concentrations of pathogens in cookie dough were tested, we also compared the total assay time required to detect 1 CFU/20 g for each assay.

Results: Culture methods were able to detect 10⁴ CFU/20g Salmonella and 10³ CFU/20g E. coli O157:H7 in 24 hours. Multiplex and real-time PCR identified both pathogens at 10⁵ CFU/20g after 8 hours and 1 hour, respectively. In order to detect 1 CFU/20g of pathogens in cookie dough, culture method required 33 hours and 36 hours for Salmonella and E. coli O157: H7, respectively. Multiplex PCR were able to detect 1 CFU/20 g of pathogens in 14 to 20 hours including enrichment. For real-time PCR, 1 CFU/20g of both pathogens were detected in 14 hours.

Significance: This study demonstrated that culture method and both PCR methods were reliable to detect Salmonella and E. coli O157:H7 in raw cookie dough. However, PCR-based methods were able to detect pathogens in cookie dough more rapidly than culture-based method. PCR-based methods would be a alternative to standard culture-based method for pathogen identification.