Comparison of an isothermal amplification and bioluminescence detection of DNA method and ISO 6579:2002 for the detection of Salmonella enterica serovars in retail meat samples.

The aim of the study was the comparative evaluation of a method based on the isothermal amplification and bioluminescence detection of the DNA (IMBD) of Salmonella vs ISO 6579:2002 in retail meat products of unknown contamination status. A total of 200 meat samples were tested. They were constituted by 116 minced meat and meat preparations to be eaten cooked (52 chicken, 48 pork and 16 beef samples) and 84 fresh meat samples (68 poultry and 16 pork). Considering both methods, 21 (10.5%) samples were positive for S. enterica. Fifteen samples were positive by both methods (71.4% of all positives); two more samples (9.5%) were found positive by the IMBD method only and four (19.1%) by the ISO 6579 method only. One ISO-positive sample was inhibited in the alternative method. For the IMBD method relative accuracy was 97.0% (95% C.I. 93.6% - 98.9%), relative sensitivity was 78.9% (95% C.I. 54.4% - 93.9%) and relative specificity was 98.9% (95% C.I. 96.1% - 99.7%). Time to negative results was shorter by the alternative method (20-24 h). Also positive results were available in 20-24 h, but they should be confirmed using other methods (“presumptive positive” results). Rapidity of response of the IMBD method gave us the opportunity to test the presumptive positive samples by MPN, which was not performed for ISO-only positive samples, due to likely microbial changes during the long storage (5-7 days) at refrigeration temperature. Salmonella MPN values in naturally contaminated meat were low, ranging between <0.3MPN/g and 2.1 MPN/g.