Development and evaluation of loop-mediated isothermal amplification, and Recombinase Polymerase Amplification methodologies, for the detection of Listeria monocytogenes in ready-to-eat food samples

Listeriosis continues to be a major health issue. This is demonstrated by the fact that, even though efforts have been made, its incidence does not decrease. Furthermore, in Europe, over 2014 a 30% increase was reported respect to 2013. In the present study two isothermal DNA amplification methods, one based on Loop-mediated isothermal AMPlification (qLAMP), and the other on Recombinase Polymerase Amplification (RPA), were developed and extensively evaluated. Both techniques demonstrated their reliability to detect Listeria monocytogenes in different types of foods. The method included a two-step enrichment, which additionally reduces the chances of detecting dead bacteria. Over the evaluation with pure bacterial DNA, the qLAMP and RPA methods resulted 10 to 100 times less sensitive than qPCR (with two different detection chemistries), but when tested in real food samples the results showed very good concordance with those obtained by qPCR and by selective agar plating (index kappa of concordance between 0.90 and 0.95). Additionally, a very low limit of detection (below 10 CFU/25 g) was obtained. Thus the optimal performance of both isothermal techniques, and their adequacy for their implementation in the food industry, was demonstrated.