Purpose: The purpose of these internal studies was to evaluate the new system as compared to the FDA/BAM or USDA/FSIS-MLG methods for pet foods, raw ground meats, raw vegetables, processed meats, chicken rinses and environmental samples and with a diverse population of known Salmonella serotypes and non-Salmonella microorganisms.
Methods: Approximately 40 samples for each matrix group were evaluated with a strain of Salmonella at <5 CFU/25g or uninoculated with the new system and reference methods for recovery. In addition, raw ground beef and chicken were evaluated with 20 fractionally spiked replicates and 5 control replicates per food. Testing was also done with 105 Salmonella serotypes and 32 non-Salmonella strains. For the new system, samples and strains were enriched in Salmonella Enrichment Base containing Salmonella Enrichment Supplement at 41.5°C. For low microbial load foods, enrichments were sampled at 18 hours. For high microbial load foods and strains, 0.1 ml samples of the primary cultures were transferred into 10 ml of R-V R10 broth and incubated at 41.5°C for 8 hours. All enrichments were streaked onto the new plating medium and incubated 41.5°C for 22 hours. Plates were subsequently tested with the Salmonella Express Confirmation Disk for 4 hours at 41.5°C.
Results: No significant differences were observed between the new system and the reference methods as indicated by Mantel-Haenszel chi-square analysis or Student’s t-test for all sample matrices. The new test system showed sensitivity and specificity of >98% among the pure culture strains.
Significance: For all matrices evaluated, the Petrifilm Salmonella Express System gave equivalent results to the reference methods for the rapid detection and biochemical confirmation of Salmonella within the procedures recommended time frame.