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A Rapid Method for the Pre‐Enrichment and Detection of Salmonella Typhimurium by Immunomagnetic Separation and Subsequent Fluorescence Microscopical Techniques

Detection of food‐borne pathogens is of great importance in order to minimize the risk of infection for customers. These analyses should be as fast as possible. Any detection method requires enrichment and quantitative analysis of the enriched microbes. Conventional enrichment methods, which take several days, need to be replaced by faster techniques such as immunomagnetic separation (IMS). This technique is based on the use of paramagnetic microspheres coated with antibodies as ligands that have specific affinity to the microbes that have to be detected. In the studies reported here, a rapid method for the detection of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium), combining IMS and Direct Epifluorescence Filter Technique (DEFT), was developed. It was focused on releasing the target cells from the magnetic beads after IMS, because this is a premise for combining IMS, as an alternative pre‐enrichment, with DEFT. Otherwise, the high number of beads form a layer on the filter membrane that makes the following microscopic analysis for the detection of the contaminants impossible. The CELLectionTM Dynabeads® used in this study, are coated with recombinant streptavidin (rSA) via a DNA linker. The rSA binds biotinylated antibodies that are able to capture target cells. The DNA linker provides the cleavable site, so that the beads can be removed from the captured cells after isolation. In this study a releasing procedure was developed. This procedure allows for an average 74 % ± 4 % of the bead‐bound Salmonella Typhimurium cells to be released from the beads after IMS, so that the detection of the separated cells by DEFT will be possible.