Purpose: The objective was to identify the best enrichment broth to simultaneously enrich Salmonella Typhimurium, E. coli O157:H7 and L. monocytogenes in seafood and spices for a multiplex qPCR detection assay.
Methods: Salmonella Typhimurium, E. coli O157:H7 and L. monocytogeneswere co-inoculated in a 1:1:1 ratio into 25g of tuna or red pepper spice blended with 225g of a candidate enrichment broth. Candidate broths included BAM media such as Buffered Listeria Enrichment Broth (BLEB) and modified Buffered Peptone Water (mBPW), published research broths including SEL, an FDA Research Broth (BMW) and modifications of these broths. After 24h incubation at 35°C, multiplex qPCR was performed on DNA extracts for pathogen detection.
Results: All target pathogens were detected in tuna enrichment in all candidate broths. Variations in Ct values for Salmonella Typhimurium and E. coli O157:H7 between the candidate broths were significantly different (P <0.05). For example, E. coli O157:H7 Ct values ranged from 24.11±0.52 in mBPW+glucose to 36.1±6.25 in UPB (n=3). In red pepper, L. monocytogenes was not detected in BMW, Buffered BMW, mBPW and SSL broth enrichment. Salmonella Typhimurium, E. coli O157:H7, and L. monocytogeneshad Ct values of 29.26±2.09, 28.59±2.07 and 35.85±0.86, respectively, in red pepper mBPW+glucose enrichment.
Significance: The results will impact regulatory microbiological methods for the detection of multiple microbial target pathogens from foods and will provide a less labor intensive means for pathogen screening.