Purpose: To evaluate performance of the molecular method after improvements were made. Molecular method performance was compared to that of either the USDA-FSIS or FDA/BAM reference culture methods for ice cream, peanut butter, dry dog food, raw ground turkey, raw ground beef, and sponge samples from a stainless steel surface.
Methods: For both the molecular and reference methods, 40 test portions of each food product were inoculated with Salmonella spp. at a level to produce fractional positive results, along with 5 high level samples and 5 uninoculated controls. Half of the test portions were analyzed by the molecular method after 16 h and 24 h enrichment and half by the reference procedure.
Results: All high level samples tested positive and all negative controls tested negative for each food product by both molecular and reference methods. At the fractional positive level, a total of 120 test portions were analyzed by each method. There were a total of 75 positive results by the molecular assay and 80 by the reference procedures. There were no statistically significant differences in the number of positive results obtained by the alternative and reference methods for any of the products tested as determined by probability of detection analysis.
Significance: A modification to the reagent formulation and a minor procedural change to the molecular method did not affect performance of the assay. Enhanced reagent formulation provided increased pellet solubility, thus eliminating any need for pipette mixing of the lysed sample and assay reagents. This improved operator ease of use, while minimizing the risk of contamination.