Quantification of Salmonella spp, Listeria monocytogenes and Escherichia coli O157 H7 in non-spiked food products and evaluation of real-time PCR as a diagnostic tool in routine food analysis

Escherichia colt O157 H7 Listeria monocytogenes and Salmonella spp are foodborne pathogens frequently associated with foods such as poultry ready-to-eat products fruits and vegetables PCR-based procedures are rapid sensitive and accurate in particular real-time PCR (qPCR) which besides being an automated high-throughput technique allows quantification of foodborne pathogens In the present work qPCR-based methods were applied for the quantitative detection of E coli O157 H7 Salmonella spp and L monocytogenes in a total of 306 non-spiked food samples in a study carried out in two laboratories simultaneously qPCR allowed the detection of the three pathogens in around 20% of the analyzed samples for each pathogen Quantification results revealed the presence of the three pathogens mostly at levels between 10(2) and 10(4) cells/g Besides quantification the qPCR results (presence/absence) were compared with those of the standard mini-VIDAS system In order to determine which were the "true positive samples conventional PCR was carried out after the corresponding enrichment for each pathogen These results were considered as the gold standard for further analysis The statistical analysis of global data recording the presence of E colt O157 H7 and L monocytogenes together with data previously obtained for Salmonella spp revealed that qPCR outperformed the mini-VIDAS procedures in terms of both time and accuracy Thus these results proved qPCR to be useful as a rapid diagnostic test for the direct detection of pathogens in food without the need for enrichment steps (C) 2010 Elsevier Ltd All rights reserved