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Culture-independent quantification of Salmonella enterica in carcass gauze swabs by flotation prior to real-time PCR
DTU Technical University of Denmark, Denmark.ORCID iD: 0000-0001-6492-1245
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2011 (English)In: International Journal of Food Microbiology, ISSN 0168-1605, E-ISSN 1879-3460, Vol. 145, no SUPPL. 1, p. S103-S109Article in journal (Refereed) Published
Abstract [en]

To facilitate quantitative risk assessment in the meat production chain, there is a need for culture-independent quantification methods. The aim of this study was to evaluate the use of flotation, a non-destructive sample preparation method based on traditional buoyant density centrifugation, for culture-independent quantification of intact Salmonella in pig carcass gauze swabs (100cm2) prior to quantitative PCR (qPCR). A novel approach was investigated, excluding the homogenization step prior to flotation, to improve the detection limit and speed up the quantification procedure. The buoyant density of two Salmonella strains in different growth conditions was determined to be 1.065-1.092g/ml. Based on these data, an optimal discontinuous flotation with three different density layers, ~1.200, 1.102 and 1.055g/ml, was designed for extracting intact Salmonella cells from pig carcass swabs. The method allowed accurate quantification from 4.4×102 to at least 2.2×107CFU Salmonella per swab sample using qPCR (without preceding DNA extraction) or selective plating on xylose lysine deoxycholate agar. Samples with 50CFU could be detected occasionally but fell outside the linear range of the standard curve. The swab samples showed a broad biological diversity; for seven samples not inoculated with Salmonella, the microbial background flora (BGF) was determined to 5.0±2.2 log CFU/ml sample withdrawn after flotation. It was determined that the proceeding PCR step was inhibited by BGF concentrations of ≥6.1×108CFU/swab sample, but not by concentrations ≤6.1×106CFU/swab sample. By using the gauze swabs directly in the flotation procedure, the homogenization step normally used for preparation of food-related samples could be excluded, which simplified the culture-independent quantification method considerably. © 2010 Elsevier B.V.

Place, publisher, year, edition, pages
2011. Vol. 145, no SUPPL. 1, p. S103-S109
Keywords [en]
Buoyant density, Centrifugation, Food analysis, Food microbiology, Food safety, Meat, article, bacterial strain, carcass, cell density, colony forming unit, evaluation, flotation, gauze dressing, nonhuman, quantitative analysis, real time polymerase chain reaction, risk assessment, Salmonella enterica, swine, Animals, Polymerase Chain Reaction, Salmonella, Suidae
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-39023DOI: 10.1016/j.ijfoodmicro.2010.03.042Scopus ID: 2-s2.0-79953058634OAI: oai:DiVA.org:ri-39023DiVA, id: diva2:1324774
Note

Funding details: Svenska Forskningsrådet Formas, 222-2007-373; Funding details: Royal Swedish Academy of Sciences; Funding details: European Commission, FOOD-2006-CT-036272; Funding details: Kungl. Skogs- och Lantbruksakademien; Funding text 1: Kirsten Michaëlis is acknowledged for excellent technical assistance. The swab samples were kindly provided by the Danish meat producer Danish Crown and the BactXtractor medium by FertiPro, Belgium. This study was financially supported by the European Union project BIOTRACER ( FOOD-2006-CT-036272 ), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning ( 222-2007-373 ) and the Royal Swedish Academy of Agriculture and Forestry (KSLA, Foundation: Carl-Fredrik von Horn), Stockholm, Sweden .

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-14Bibliographically approved

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