Purpose: The aim of this study was to compare a newly developed molecular method to the traditional ISO cultural method for detection of Listeria, including L. monocytogenes, in raw animal proteins.
Methods: Raw refrigerated meat, poultry, fish and seafood samples (n = 66) were obtained from sources in France and the USA. Samples were naturally contaminated with Listeria or were artificially contaminated using a variety of Listeria monocytogenes isolates. Samples were analyzed using the cultural ISO 11290-1 method and using the new molecular method. For the new method, samples were diluted 1:20 in demi-Fraser broth, incubated for 28 h and subsequently tested using a modification of existing molecular detection methods. All presumptive results from the new methods were confirmed from enrichment broth onto selective and differential agars with further testing per ISO.
Results: Results for the two methods agreed for 45 of the 66 samples. The new molecular method detected 18 positive samples that were not identified by the ISO cultural method, and only missed three positives that were identified by the ISO method.
Significance: Disagreements between two test methods may occur due to contaminant distribution and other factors, but if methods are equivalent, a balanced ratio of positive to negative disagreements is expected. This study found enhanced detection by the new molecular method for Listeria in raw animal proteins, relative to the ISO cultural method, evidenced by an imbalance between positive and negative disagreements. This improved performance is available as a next-day result, compared to the ISO method which takes over one week.