Detection of Salmonella spp. from large volumes of water by modified Moore swabs and tangential flow filtration

This study compares the use of tangential flow filtration (TFF), normal flow filtration and modified Moore swabs (MMS) for the concentration and detection of Salmonella, spiked at 1–760 CFU l−1, from 10 l of surface water. Two immunomagnetic separation (IMS) methods, Pathatrix and Dynabeads, for further concentration of Salmonella were compared following filtration and overnight enrichment. Detection of Salmonella by PCR, qPCR or culture-based methods was compared. TFF and MMS preformed equally well in concentrating Salmonella. MMS was able to consistently concentrate Escherichia coli O157:H7 for culture-based detection; only at the higher concentrations tested was the TFF able to consistently concentrate E. coli O157:H7 for culture-based detection. Salmonella, at population densities <10 CFU l−1 in 10 l of spiked surface water, could be reliably (6/6) detected within 2 days by combining TFF or MMS, with IMS Pathatrix and qPCR. The theoretical limit of detection for Salmonella is considered to be sufficiently sensitive to meet all the practical screening purposes for surface waters in an agricultural setting intended for application to edible horticultural crops. Significance and Impact of the Study Large-volume water samples may be screened for the presence of Salmonella both preseason and preharvest. This will provide better data from which to make risk management decisions to improve fresh produce safety. The time required to complete screening (2 days) will make it more practical to screen surface waters for Salmonella prior to use during produce production, to facilitate source tracking in root-cause determination or to determine risk associated with water nearby produce fields. The method enables the direct screening for pathogens in a timely manner, which avoids the need to rely on indicator or index organisms to evaluate food safety risks. Use of this method has the potential to decrease the risk of in-field fresh produce contamination.