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Culture-independent quantification of Salmonella enterica in carcass gauze swabs by flotation prior to real-time PCR

Löfström, Charlotta LU ; Schelin, Jenny LU ; Norling, Borje; Vigre, Hakan; Hoorfar, Jeffrey and Rådström, Peter LU (2011) In International Journal of Food Microbiology 145. p.103-109
Abstract
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 (100 cm(2)) 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 1.065-1.092 g/ml. Based on these data, an optimal... (More)
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 (100 cm(2)) 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 1.065-1.092 g/ml. Based on these data, an optimal discontinuous flotation with three different density layers, similar to 1.200, 1.102 and 1.055 g/ml, was designed for extracting intact Salmonella cells from pig carcass swabs. The method allowed accurate quantification from 4.4 x 10(2) to at least 2.2 x 10(7) CFU Salmonella per swab sample using qPCR (without preceding DNA extraction) or selective plating on xylose lysine deoxycholate agar. Samples with 50 CFU 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 x 10(8) CFU/swab sample, but not by concentrations <= 6.1 x 10(6) CFU/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. (C) 2010 Elsevier B.V. All rights reserved. (Less)
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author
organization
publishing date
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Contribution to journal
publication status
published
subject
keywords
Buoyant density, Centrifugation, Meat, Food analysis, Food safety, Food, microbiology
in
International Journal of Food Microbiology
volume
145
pages
103 - 109
publisher
Elsevier
external identifiers
  • wos:000289819900017
  • scopus:79953058634
ISSN
0168-1605
DOI
10.1016/j.ijfoodmicro.2010.03.042
language
English
LU publication?
yes
id
2220d295-6662-4a1b-969c-1dd7e56d18e7 (old id 1964980)
date added to LUP
2011-05-23 12:17:53
date last changed
2017-11-05 03:21:38
@article{2220d295-6662-4a1b-969c-1dd7e56d18e7,
  abstract     = {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 (100 cm(2)) 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 1.065-1.092 g/ml. Based on these data, an optimal discontinuous flotation with three different density layers, similar to 1.200, 1.102 and 1.055 g/ml, was designed for extracting intact Salmonella cells from pig carcass swabs. The method allowed accurate quantification from 4.4 x 10(2) to at least 2.2 x 10(7) CFU Salmonella per swab sample using qPCR (without preceding DNA extraction) or selective plating on xylose lysine deoxycholate agar. Samples with 50 CFU 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 &gt;= 6.1 x 10(8) CFU/swab sample, but not by concentrations &lt;= 6.1 x 10(6) CFU/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. (C) 2010 Elsevier B.V. All rights reserved.},
  author       = {Löfström, Charlotta and Schelin, Jenny and Norling, Borje and Vigre, Hakan and Hoorfar, Jeffrey and Rådström, Peter},
  issn         = {0168-1605},
  keyword      = {Buoyant density,Centrifugation,Meat,Food analysis,Food safety,Food,microbiology},
  language     = {eng},
  pages        = {103--109},
  publisher    = {Elsevier},
  series       = {International Journal of Food Microbiology},
  title        = {Culture-independent quantification of Salmonella enterica in carcass gauze swabs by flotation prior to real-time PCR},
  url          = {http://dx.doi.org/10.1016/j.ijfoodmicro.2010.03.042},
  volume       = {145},
  year         = {2011},
}