Evaluation of a PCR‐ELISA for food testing: Detection of selectedSalmonellaserovars in confectionery products

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Abstract
A specific PCR‐ELISA detection system was established for the testing of food products for Salmonella contamination. Initially a shortened microbial enrichment comprising two steps, a non‐selective and selective incubation each of 8 hours at 37°C, is carried out. DNA is then isolated from 1 ml of the final selective enrichment culture and purified. In vitro amplification of the recovered DNA is performed in a competitive PCR in the presence of internal standard DNA to exclude the possibility of false negative results arising from food‐borne inhibitory factors. Salmonella specific amplicons were identified through specific probe hybridization and colorimetric endpoint detection in a microtiter plate, a format which allows a high throughput due to its high potential for automation. The PCR‐ELISA was validated and compared to conventional microbiological methods according to FDA and LMBG §35 requirements. 127 of 480 food samples were artificially contaminated with different serovars (Enteritidis, Typhimurium, Senftenberg, Tennessee, Agona) at varying doses of up to 5 × 106 cfu per 750 g sample. In conclusion 122 samples were evaluated by each method as Salmonella positive, all of which were from Salmonella spiked food samples. The PCR‐ELISA with a detection limit of ≤ 10 cfu/750g enables considerable reduction of the analysis duration of 24 hours without compromising reliability.