Comparison of the FDA BAM Salmonella Method and a New PCR Method for Detection of Salmonella Species in Spices

Introduction: Contamination of spices with Salmonella spp. can cause expensive and commercially damaging product recalls of batches of spices, semi-finished and finished food products. Many current detection methods for Salmonella are cumbersome and slow to provide results.  The Thermo Scientific™ SureTect™ Salmonella species PCR Assay, a new method for the detection of Salmonella, enables results to be achieved in less than 24 h compared to 6-7 days for culture-based methods.

Purpose: To compare the FDA BAM and SureTect PCR methods to detect Salmonella from 375-g samples of powdered chili, onion and garlic.

Methods: Seven samples of chili consisting of 2 unspiked and 5 spiked (at 22.2 CFU), fourteen samples of onion; consisting of 3 unspiked and 11 spiked samples (ranging from 12.8 to 112 CFU) and 11 samples of garlic; consisting of 3 unspiked and 8 spiked samples (ranging from 3.4 CFU to 49 CFU) were prepared and incubated in Tryptone Soya Broth (TSB) at 35°C for 20 - 22 h according to the FDA BAM method (including adjustment of pH and addition of potassium sulphite, where required). Following incubation, samples were removed for analysis with the new PCR assay, then analyzed and confirmed as detailed in the kit instructions. TSB enrichments were also sub-cultured into selective broths and processed according to the FDA BAM method. Finally, presumptive positive results from all plating media were confirmed using a Salmonella latex kit.

Results: All unspiked and spiked samples analyzed returned results which were in complete agreement between the two methods compared in this study. No examples of false negative or false positive results were obtained by the PCR assay and PCR inhibition was not observed.

Significance: The results gained in this study demonstrated that the PCR method is an accurate and reliable alternative to the FDA BAM method for the detection of Salmonella from spices.