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 co mmercially-available and laboratory-prepared antibodies, followed by a n enrichment stage and end-point detection by ELISA. IMS alone gave an average of 77% recovery of cells artificially inoculated into the foo d, and a range of 20-110% recovery, depending on food type. The combin ed model system (IMS-ELISA) enables detection of either < 10 cells m(- 1) whole egg extract (using overnight enrichment after IMS), or >10 ce lls ml(-1) (3 h enrichment after IMS). Cross-reactivity of antibodies with Citrobacter was decreased by using two different immunochemical s teps: IMS with monoclonal antibody-coated beads, and a 'sandwich' ELIS A with polyclonal capture antibody and monoclonal detector antibody. D iscussion is presented on the best food preparation method, optimal su bstrate type for the ELISA and on the potential of IMS.