Short communicationLoop-mediated isothermal amplification (LAMP) coupled with bioluminescence for the detection of Listeria monocytogenes at low levels on food contact surfaces
Introduction
Listeria monocytogenes, a foodborne pathogen, is responsible for nearly 1600 illnesses (listeriosis) annually in United States, resulting in 260 deaths (Scallan et al., 2011). Food contact surfaces, like stainless steel (SS) or polyethylene (PE), are known to be the major routes of cross-contaminations with L. monocytogenes (Verran, Airey, Packer, & Whitehead, 2008) and were associated with several outbreaks related to the food industry, especially in salmon processing plants (Tocmo et al., 2014). Organic residues on these surfaces increase the persistence of L. monocytogenes (Chasseignaux et al., 2002, Takahashi et al., 2011) and might affect the results of the applied detection methods used for hygiene monitoring (Martinon, Cronin, Quealy, Stapleton, & Wilkinson, 2012).
Therefore, the objective of this study was to evaluate the performance of a commercial loop-mediated isothermal DNA amplification (LAMP) based method with bioluminescence named as 3M™ Molecular Detection System (MDS) for the detection of L. monocytogenes on stainless steel (SS) and polyethylene (PE) using the 3M™ Molecular Detection Assay (MDA). The study was conducted for the detection of low inoculum levels of L. monocytogenes in comparison to the International Organization for Standardization (ISO) method to validate LAMP-based method. The influence of organic load (OL) presence was also studied on the survival of L. monocytogenes on tested surfaces and/or LAMP-based system performance (Fig. 1).
Section snippets
Cultures preparation
L. monocytogenes serovars 1/2a (ATCC BAA 679), 1/2b (ATCC BAA 839) and 4b (ATCC 13932), from American Type Culture Collection (Manassas, VA, USA), were activated in 10 ml of tryptone soya broth (TSB, Oxoid, Basingstoke, Hampshire, UK) for 24 h at 37 °C. The cultures were centrifuged at 3500g for 10 min at 4 °C, washed twice with 0.1% (w/v) peptone water (PW, Oxoid, Basingstoke, Hampshire, UK), and resuspended in 1 ml of 0.1% (w/v) PW (Oxoid), and then mixed (1:1:1, v/v/v) to prepare a 3-strain
Results and discussion
In this study, a 3-strain cocktail of Listeria monocytogenes isolates from different origins (animal and clinical specimens) was used in order to avoid the strain-specific effects on the detection of L. monocytogenes. All control surfaces with and without (w/o) organic load (OL) were negative for ISO and LAMP-based methods (data not shown). At the inoculum level of 100 CFU/100 cm2, both methods were unable to detect L. monocytogenes, regardless of OL presence and surface type (Table 1). At 101
Conclusion
This study showed that LAMP-based system provides rapid and reliable results for the detection of L. monocytogenes at low levels on both clean and contaminated food processing surfaces, and can be applicable in seafood industry.
Acknowledgements
The authors would like to acknowledge 3M Food Safety, Asia Pacific Pte Ltd. for financial support.
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Permanent address. Chair of Industrial and Food Microbiology, Faculty of Food Science, University of Warmia and Mazury in Olsztyn, Plac Cieszyński 1, 10-726 Olsztyn, Poland.