Purpose: We, thus, employed a strategy that uses extended enrichment times to evaluate a gold standard method for detection of Salmonella (i.e., the FDA BAM method) in dry pet food inoculated at fractional positive levels.
Methods: This evaluation was performed with five Salmonella strains (each tested in 20 replicates) that were selected due to their poor ability to grow in enrichment media and to be detected by the rapid detection method.
Results: Four samples that were negative with the standard BAM method, but positive with the extended BAM method (for example after primary enrichment of 72 h rather that the standard 24 h). These data indicated a false negative rate, determined by the BAM method, to be 7%. By comparison, previously evaluated alternative methods showed false negative rates as low as 4%. With the new data presented here, we can now conclude that some of these previously evaluated assays showed lower or comparable false negative rates relative to the BAM method. Additional rapid methods for detection of Salmonellain dry pet food were conducted and some methods showed false negative rates in excess of 82%.
Significance: Overall, our data indicated that further stringent evaluation of standard culture-based methods will be valuable for determining the efficacy of alternative (e.g., rapid) detection methods. There still are commercial methods that produce substantial false negative rates that are clearly inferior to standard culture-based detection methods.