A new test system for Salmonella detection in food products by competitive immonoassay

Detecting Salmonella in foods is topical due to the known cases of salmonellosis epidemics. Immunochemical methods including enzyme-linked immunosorbent assay (ELISA) have been widely used in Salmonella detection. Traditionally, ELISA of Salmonella is based on detecting lipopolysaccharide (LPS), which is considered to be the main structural component of the outer membrane of the cell of Gram-negative bacteria. Core (conservative LPS element common to all Salmonella) and O-antigen (hypervariable LPS element) are available for interaction with antibodies. It was shown using commercial MAb 5D12A (to the core of LPS) or MAb 10D9H (to the common epitope of the O-antigen of Salmonella serogroups A, B and D) that in the Salmonella culture obtained during sample preparation, traditional for the analysis of these bacteria in foods, LPS is present mainly outside cells, in the medium (no less than 90 %). It has been found that the addition of centrifugation to the standard sample preparation procedure to separate bacteria from the medium and a subsequent analysis of the medium can expand the test-system working range towards lower LPS concentrations and increase the analytical sensitivity. It has been shown that immobilization of the bovine serum albumin (BSA)-LPS conjugate in the wells of a microplate immunosorbent allows one to obtain a more homogeneous coating than immobilization of LPS itself. We have elaborated 2 test systems for Salmonella detection in foods by competitive ELISA of LPS secreted in medium. In each of the two test systems, the BSA-LPS conjugate is immobilized on the solid phase, and in the liquid phase there are either MAb 5D12A or MAb 10D9H. The sensitivity of the analysis for each test system is 10⁵ CFU/ml. The test system based on MAb 5D12A is advan tageous since it allows detecting all Salmonella regardless of serotype.

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