Probeliatrade mark PCR system for rapid detection of Salmonella in milk powder and ricotta cheese

The Probeliatrade mark Salmonella sp. PCR amplification and detection kits (Sanofi Diagnostics Pasteur, Marnes La Coquette, France) were evaluated for the rapid and specific detection of Salmonella agona artificially inoculated into skim milk powder and ricotta cheese. The Probeliatrade mark results were compared with those obtained using the Australian Standard Method. Using a pure culture of Salm. agona, the detection limit of Probeliatrade mark was between 8 and 79 cfu ml-1, equivalent to 0.2-2 cfu per PCR reaction. Detection of Salm. agona inoculated in skim milk powder (at 5-10 cfu g-1, stored at 5, 15 or 25 degrees C) and ricotta cheese (at 1-2, 10-20 and 100-200 cfu per 25 g) was effected by using non-selective enrichment prior to the PCR determinations. For all of the 40 milk powder samples and 12 ricotta cheese samples, the Probeliatrade mark results were consistent with those using the Australian Standard Method. Using Probeliatrade mark, Salmonella was detected to genus level in the dairy products within 24-28 h, whereas the cultural technique required 3-4 d for presumptive positive isolates and further time for confirmation.