Detection of Salmonella enterica in Meat in Less than 5 Hours by a Low-Cost and Noncomplex Sample Preparation Method.

Salmonella is recognized as one of the most important foodborne bacteria and has wide health and socioeconomic impacts worldwide. Fresh pork meat is one of the main sources of Salmonella, and efficient and fast methods for detection are therefore necessary. Current methods for Salmonella detection in fresh meat usually include >16 h of culture enrichment, in a few cases <12 h, thus requiring at least two working shifts. Here, we report a rapid (<5 h) and high-throughput method for screening of Salmonella in samples from fresh pork meat, consisting of a 3-h enrichment in standard buffered peptone water and a real-time PCR-compatible sample preparation method based on filtration, centrifugation, and enzymatic digestion, followed by fast-cycling real-time PCR detection. The method was validated in an unpaired comparative study against the Nordic Committee on Food Analysis (NMKL) reference culture method 187. Pork meat samples (n = 140) were either artificially contaminated with Salmonella at 0, 1 to 10, or 10 to 100 CFU/25 g of meat or naturally contaminated. Cohen's kappa for the degree of agreement between the rapid method and the reference was 0.64, and the relative accuracy, sensitivity, and specificity for the rapid method were 81.4, 95.1, and 97.9%, respectively. The 50% limit of detections (LOD50s) were 8.8 CFU/25 g for the rapid method and 7.7 CFU/25 g for the reference method. Implementation of this method will enable faster release of Salmonella low-risk meat, providing savings for meat producers, and it will help contribute to improved food safety.IMPORTANCE While the cost of analysis and hands-on time of the presented rapid method were comparable to those of reference culture methods, the fast product release by this method can provide the meat industry with a competitive advantage. Not only will the abattoirs save costs for work hours and cold storage, but consumers and retailers will also benefit from fresher meat with a longer shelf life. Furthermore, the presented sample preparation might be adjusted for application in the detection of other pathogenic bacteria in different sample types.

Cost-effective optimization of real-time PCR-based detection of Campylobacter and Salmonella with inhibitor tolerant DNA polymerases.

AIMS: The aim of this study was to cost-effectively improve detection of foodborne pathogens in PCR inhibitory samples through the use of alternative DNA polymerases. METHODS AND RESULTS: Commercially available polymerases (n = 16) and PCR master mixes (n = 4) were screened on DNA purified from bacterial cells in two validated real-time PCR assays for Campylobacter and Salmonella. The five best performing (based on: limit of detection (LOD), maximum fluorescence, shape of amplification curves and amplification efficiency) were subsequently applied to meat and faecal samples. The VeriQuest qPCR master mix performed best for both meat and faecal samples (LODs of 10(2) and 10(4) CFU ml(-1) in the purest and crudest DNA extractions respectively) compared with Tth (LOD = 10(2)-10(3) and 10(5)-10(6) CFU ml(-1)). AmpliTaqGold and HotMasterTaq both performed well (LOD = 10(2)-10(4) CFU ml(-1)) with meat samples and poorly (LOD = 10(3)-10(6) CFU ml(-1)/not detected) with faecal samples. CONCLUSIONS: Applying the VeriQuest qPCR master mix in the two tested real-time PCR assays could allow for simpler sample preparation and thus a reduction in cost. SIGNIFICANCE AND IMPACT OF THE STUDY: This work exemplifies a cost-effective strategy for optimizing real-time PCR-based assays. However, a DNA polymerase suitable for one assay and sample type is not necessarily optimal for other assays or sample types.