Evaluation of an immunomagnetic separation-real-time PCR assay for the rapid detection of Salmonella in meat

The aim of this study was the comparison of an immunomagnetic separation (IMS)-real time PCR assay for the detection of Salmonella with the cultural reference method according to 35 of the German Law on Food and Commodities (LMBG, L 00.00.20:1998). The IMS-real-time PCR assay includes a nonselective preenrichment step, an IMS, DNA extraction, as well as DNA purification followed by hybridization probe-based real-time PCR analysis. An accurate comparability was achieved, because both methods analyzed the same preenrichment. The evaluation was carried out using both artificially and naturally contaminated meat samples. The IMS-real-time PCR assay provides a result after 12 to 13 h. Compared with the reference method and regarding artificially contaminated meat samples, the IMS-real-time PCR assay achieved a specificity of 80% (false-positive rate of 20%) and a sensitivity of 100% (false-negative rate of 0%). The relative accuracy was 94%. The detection limit of both methods was 10 CFU/25 g. The concordance index K, which defines the statistical accordance, was 0.85 and indicated the agreement of both methods on statistical criteria. Compared to the reference method and analyzing naturally contaminated meat samples (n = 491), the IMS-real-time PCR assay showed a specificity of 99.3% (false-positive rate of 0.7%) and a sensitivity of 83.7% (false-negative rate of 16.3%). The relative accuracy was 98%. The concordance index K had a value of 0.87 and highlighted the statistical agreement of both methods. In conclusion, the IMS-real-time PCR assay is suitable as specific, sensitive, and rapid screening method for the detection of Salmonella from meat.