Optimization of the reactional medium and a food impact study for a colorimetric in situ Salmonella spp. detection method

Foodborne pathogens are still a major concern for public health authorities. In this paper, we describe the optimization of a previously reported method which combines a highly specific capture of targeted food pathogens with an intracellular staining method. The reaction medium was optimized to simultaneously allow specific enrichment of Salmonella and maximize the staining of the target pathogen. This in situ colorimetric concept was evaluated with a broad range of food samples artificially contaminated with low levels of stressed Salmonella to mimic natural contamination conditions. This direct detection method compared favorably to a commercially available immunoassay system (Vidas® UP Salmonella), for cooked meat, dry milk powder and egg products. Globally 88% agreement was obtained between the two methods with a sensitivity of 80% and a specificity of 100% for the tested method. Main discordances were obtained with food matrices having high levels of competitive Gram negative microflora. These observations show that the design of an adapted culture medium is necessary to enhance the specific in situ capture and revelation system.