Bacteriophage-based enrichment coupled to immunochromatographic strip-based detection for the determination of Salmonella in meat and poultry

Immunochemical-based methods for the detection of Salmonella in food can be complicated by the presence of closely related, immunocrossreactive non-Salmonella species in the sample that may cause false-positive results. To circumvent this problem, specific bacteriophages against immunocrossreactive, non-Salmonella bacteria were used in the sample enrichment step to suppress their growth and improve the performance of an immunochromatographic strip-based detection method for Salmonella. Cross-reactive bacteria were isolated from various food sources and were characterized with a panel of Salmonella somatic 0 antigen-specific monoclonal antibodies. These cross-reactive bacteria were primarily Citrobacter spp. and Escherichia coli with serology shared with Salmonella serogroups B, D, and E These bacteria were used as hosts for the isolation of specific lytic bacteriophages. When formulated with the primary enrichment, the bacteriophage cocktail significantly reduced false positives with a broadly reactive immunochromiatographic test strip. This was demonstrated in both artificially and naturally contaminated meat. False positives in naturally contaminated beef samples were reduced from 32 of 115 samples tested to zero. In raw meat and poultry with a relatively high bioburden (>10(5) CFU/g), the use of the bacteriophage-based enrichment procedure gave improved recovery of Salmonella compared with the conventional culture-based reference method. This was observed when coupled to either test strip-based or selective agar-based detection. The use of specific bacteriophages for the control of immunocrossreactive and competitive microflora during the food sample enrichment step provides a new approach for enhancing the performance of both immunological- and cultural-based detection methods.