Effects of Different Broth Enrichment upon Phage Magnetoelastic Biosensor for Fast Detecting Low <i>Salmonella</i> Counts on Problematic Produce

Abstract

According to the FDA Bacteriological Analytical Manual (BAM) for Salmonella identification in produce, two pre-enrichment steps with 48 hours of incubation are the golden procedures. Lactose broth is recommended for the first pre-enrichment step medium for leafy greens, and the universal pre-enrichment (UP) broth is for tomatoes. However, the suggested broths were evaluated to have the maximum performance using the culture-dependent methods, and may not be applied to other methods, such as biosensor detection platform. A wireless bacteriophage magnetoelastic (ME) biosensor has been recently developed for real-time or rapid detection of food-borne pathogens in various foods. This affinity-based biosensor utilizes a phage oligonucleotide as the probe to capture target bacteria. In this study, the efficiencies of different pre-enrichment media for early detection of low Salmonella on spinach leaves and tomatoes use ME biosensors to shorten detection time. Four broths of modified peptone water, Lennox broth (LB), lactose broth, and UP broth were selected in this study. Various pre-enrichment times for ME biosensor detection were investigated. After spiking 4 cfu/g Salmonella on the tomatoes surfaces, the phage biosensor was able to detect Salmonella within 5 hours of pre-enrichment comparing to 24 hours in the FDA procedures. For Salmonella spiked spinach leaves, the same medium showed Salmonella positive within 7 hours. This study demonstrated that LB broth is the best medium to shorten pre-enrichment time to pass Salmonella number detection thresholds for ME biosensor detection in spinach and tomatoes when comparing to FDA procedures.