Evaluation of a Method for Rapid Detection of Listeria monocytogenes in Dry-Cured Ham Based on Impedanciometry Combined with Chromogenic Agar

Abstract

The food industry is in need of rapid, reliable methodologies for the detection of Listeria monocytogenes in ready-to-eat products, as an alternative to the International Organization of Standardization (ISO) 11290-1 reference method. The aim of this study was to evaluate impedanciometry combined with chromogenic agar culture for the detection of L. monocytogenes in dry-cured ham. The experimental setup consisted in assaying four strains of L. monocytogenes and two strains of Listeria innocua in pure culture. The method was evaluated according to the ISO 16140:2003 standard through a comparative study with the ISO reference method with 119 samples of dry-cured ham. Significant determination coefficients ( R of up to 0.99) for all strains assayed in pure culture were obtained. The comparative study results had 100% accuracy, 100% specificity, and 100% sensitivity. Impedanciometry followed by chromogenic agar culture was capable of detecting 1 CFU/25 g of food. L. monocytogenes was not detected in the 65 commercial samples tested. The method evaluated herein represents a promising alternative for the food industry in its efforts to control L. monocytogenes. Overall analysis time is shorter and the method permits a straightforward analysis of a large number of samples with reliable results.

Comparative evaluation of impedanciometry combined with chromogenic agars or RNA hybridization and real-time PCR methods for the detection of L. monocytogenes in dry-cured ham

“…In a previous study carried out by our research group, an impedance measurement combined with OCLA to detect L. monocytogenes in dry-cured ham offered excellent values for RT, SP and SE (Labrador, Rota, Pérez, Herrera, & Bayarri, 2018), but the impedance measurement time was longer than in the present study (40 h vs 24 h).…”

“…In a previous study carried out by our research group, the pathogen was subjected to stressful conditions before inoculation in dry-cured ham. The detection of L. monocytogenes was not influenced by previous stress (Labrador, Rota, Pérez, Herrera, & Bayarri, 2018). This demonstrated that preenrichment media allowed the recovery and multiplication of the pathogen.…”

“…Impedance measurement followed by OCLA with the purpose of detecting L. monocytogenes in dry-cured ham has been previously studied in our laboratory (Labrador, Rota, Pérez, Herrera, & Bayarri, 2018). Excellent values of relative trueness, specificity and sensitivity were obtained.…”

“…They need efficient tools to control this pathogen, in order to comply with food safety regulations while minimizing economic losses. Different rapid methods have been developed for detection of L. monocytogenes such as immunoassays, fluorescent in situ hybridization, amplification methods or impedanciometry (Cho & Irudayaraj, 2013;Fuchizawa, Shimizu, Ootsubo, Kawai, & Yamazaki, 2009;Labrador, Rota, Pérez, Herrera, & Bayarri, 2018;Rodriguez-Lazaro, Gonzalez-Garcia, Gattuso, Gianfranceschi, & Hernandez, 2014). The impedance method…”