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Evaluation of a loop-mediated isothermal amplification method for the detection of Listeria monocytogenes in dairy food

Erica Tirloni, Cristian Bernardi, Sandro Drago, Giuseppe Stampone, Francesco Pomilio, Patrizia Cattaneo, Simone Stella
  • Erica Tirloni
    Department of Health, Animal Science and Food Safety, University of Milan, Italy | erica.tirloni@unimi.it
  • Cristian Bernardi
    Department of Health, Animal Science and Food Safety, University of Milan, Italy
  • Sandro Drago
    Enbiotech srl, Palermo, Italy
  • Giuseppe Stampone
    Enbiotech srl, Italy
  • Francesco Pomilio
    Institute for Experimental Veterinary Medicine of Abruzzo and Molise G. Caporale, National Reference Laboratory for Listeria monocytogenes, Italy
  • Patrizia Cattaneo
    Department of Health, Animal Science and Food Safety, University of Milan, Italy
  • Simone Stella
    Department of Health, Animal Science and Food Safety, University of Milan, Italy

Abstract

Objective of the present study was to test the performances of a loop-mediated isothermal amplification (LAMP)-based method for the detection of Listeria monocytogenes, with particular focus on the dairy products. The specificity of the method was evaluated on 42 different Listeria spp. strains from collections, food and environmental samples. 100% (32 of 32) of the L. monocytogenes strains were correctly recognised, and none of other 10 Listeria spp. strains was misidentified. The sensitivity was evaluated on four L. monocytogenes strains from different sources. The instrument was able to detect 10-400 CFU/mL. The ability to detect low initial numbers of L. monocytogenes (0.3- 0.7 Log CFU/g) was also evaluated, in duplicate, in pasteurised milk (whole and skimmed) and dairy samples (fresh ricotta, crescenza, mascarpone, mozzarella, cottage cheese, cream cheese, taleggio, gorgonzola). The analysis was performed after 18, 24 and 48 h of incubation, and was coupled with the count of L. monocytogenes in the broth. Microbial loads were insufficient to achieve a positive result after 18 and 24 h in most of the samples; after 48 h, all the products, except taleggio and one gorgonzola sample, were identified as positive; the sensitivity of the method when applied to contaminated dairy foods was about 5 Log CFU/g. The LAMP method tested can be considered a very useful tool, as it is a costeffective and easy-functioning method. The preliminary data obtained should be confirmed with a validation process taking into account different food typologies.

Keywords

LAMP, Listeria monocytogenes, RTE dairy food, limit of detection

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Submitted: 2017-07-07 20:04:41
Published: 2017-12-14 11:32:47
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Copyright (c) 2017 Erica Tirloni, Cristian Bernardi, Sandro Drago, giuseppe stampone, Francesco Pomilio, Patrizia Cattaneo, Simone Stella

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