Purpose: The objective of this study is to identify the best medium for simultaneous enrichment of Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in leafy greens for a multiplex qPCR-based detection.
Methods: Salmonella Typhimurium, E. coli O157:H7, Listeria monocytogenes were co-inoculated into 25 g of baby spinach and 225 ml of pre-enrichment broth. Candidate media included BAM media such as Universal Pre-Enrichment Broth (UPB) and Tryptone Soy Broth (TSB), published research broths including, SEL, SSL, a FDA Research Broth (BMW) and modifications of these broths. After 24 h incubation at 37°C, DNA was extracted for multiplex qPCR analysis.
Results: Results show that the target pathogens were simultaneously enriched in spinach using all candidate broths. Ct values were significantly higher (P<0.05) for the enrichment of Listeria monocytogenes as compared to Salmonella Typhimurium and E. coli O157:H7 in all broths with the exception of SEL and mBPW+glucose, whereby lower Ct values for Listeria monocytogenes indicate greater enrichment. For example, Ct values for Salmonella Typhimurium, E. coli O157:H7 and Listeria monocytogenes were 26.98±0.58, 26.98±0.58, and 34.67±4.21, respectively, in SSL, as compared to 24.92±0.95, 24.92±0.50 and 29.89±0.65, respectively, in mBPW+glucose.
Significance: The results will improve current regulatory microbiological methods encompassing the recovery, enrichment, and detection of multiple microbial pathogens from foods to provide a less labor intensive means to sample preparation and pathogen screening.