Purpose: The purpose of this internal evaluation was to compare the new method to the FDA/BAM for frozen uncooked shrimp, fresh spinach, dry dog food and stainless steel; to the USDA/FSIS-MLG method for raw ground chicken, pasteurized liquid whole egg, raw ground beef, raw ground pork and cooked chicken nuggets; and to the ISO 6579 method for raw ground chicken and liquid whole egg.
Methods: Each matrix was inoculated with a different strain of Salmonella and 20 replicates were analyzed at one inoculum level: 0.2-2 CFU/test portion. Five control replicates were analyzed at 0 CFU/test portion. For the new method, replicates were enriched in the Salmonella Enrichment Base containing Salmonella Enrichment Supplement for 18-24 hours at 41.5 ± 1oC. For foods with low microbial loads, test portions were streaked onto Petrifilm SALX after 18 and 24 hours broth incubation. For foods with high microbial loads, 0.1 mL of the primary enrichment was transferred into 9.9 mL of Rappaport-Vassiliadis R10 (RV[R10]) broth at both 18 and 24 hours of primary enrichment and incubated at 41.5 ± 1oC. Samples were streaked at 8 and 24 hours.
Results: No significant differences were observed between the new method and the reference methods as indicated by Mantel-Haenszel chi-square analysis and the probability of detection (POD) for all 9 matrixes.
Significance: For all foods evaluated, the Petrifilm Salmonella Express System demonstrated comparable results to the reference methods for the rapid detection and biochemical confirmation of Salmonella.