Combined immunomagnetic separation and detection of Salmonella enteritidis in food samples

A model system for immunochemical detection of Salmonella enteritidis has been developed, using immunomagnetic separation (IMS) with both commercially-available and laboratory-prepared antibodies, followed by an enrichment stage and end-point detection by ELISA. IMS alone gave an average of 77% recovery of cells artificially inoculated into the food, and a range of 20-110% recovery, depending on food type. The combined model system (IMS-ELISA) enables detection of either < 10 cells m(-1) whole egg extract (using overnight enrichment after IMS), or >10 cells ml(-1) (3 h enrichment after IMS). Cross-reactivity of antibodies with Citrobacter was decreased by using two different immunochemical steps: IMS with monoclonal antibody-coated beads, and a 'sandwich' ELISA with polyclonal capture antibody and monoclonal detector antibody. Discussion is presented on the best food preparation method, optimal substrate type for the ELISA and on the potential of IMS.