Purpose: The objective of this work was to define and to evaluate an enrichment protocol suitable for PPS samples allowing the next day detection of Salmonella with the assay.
Methods: Faecal samples from pigs and poultry were enriched for 16 to 24 h at 41.5 °C in buffered peptone water supplemented with different selective agents, tested at different concentrations, prior to performing the assay. Transfer to a selective broth, Salmonella Xpress2 broth (SX2) was also studied with an incubation period between 6 and 24 hours at 41.5 °C. Positive results were confirmed by streaking the broths onto selective agar. The ISO 6579/A1 method was used as the reference method.
Results: Among all the supplements tested, the proprietary Salmonella supplement provided the best recovery of Salmonella but at double the concentration used for analysis of food samples. A transfer into the selective SX2 broth was also necessary to avoid false-negative results. A transfer of 1 ml into 10 ml of SX2 broth gave better results than 0.1 ml or even 0.5 ml, and incubation for 6 hours at 41.5 °C was comparable to 24 hours. Of the 154 products tested, the new method provided 81 positive results compared to 69 for the reference method. Overgrowth of plates by competing flora was an issue and the SALSA plate gave the best recovery. In some cases, a second transfer in SX2 broth before streaking, was necessary for confirmation.
Significance: The new enrichment protocol for the Salmonella assay provided better results than the ISO 6579/A1 reference method for the detection of Salmonella in environmental samples of the PPS, allowing release of negative products in less than 26 hours.