Preliminary results on prevalence and persistence of Listeria monocytogenes in different dairy and meat processing plants in Central Italy

Abstract

Purpose: Listeria monocytogenes is a relevant food - borne pathogen able to cause severe and fatal infections in humans. Understanding correlations among different Listeria monocytogenes strains and evaluating Listeria monocytogenes isolates capacity to persist in processing plant environments is an essential tool for food surveillance. Most outbreaks of human listeriosis seem to be linked to strains able to persist in the environment and to replicate in foods. The aim of this study was to investigate prevalence and persistence of Listeria monocytogenes strains subtypes in different dairy and meat processing plants in the Abruzzo and Molise Region. Methods & Materials: Totally 14 food processing plants have been selected for the study (7 for dairy products – DP - and 7 for meat products - MP). Sampling was performed in 4 session from March to October 2017, from 30 to 35 environmental sampling have been sampled in all the division of the plants, both from food contact surfaces (FCS) and non food contact surfaces (NFCS). Sampling sites were selected as niches for Listeria monocytogenes presence. Samples were tested with FSIS MLG8-10:2017 method. Listeria monocytogenes strains were serotyped using the method described in the U.S. FDA Bacteriological Analytical Manual (Bennett and Weaver, 2001). PFGE subtyping was performed according to the PulseNet protocol (Pulsenet USA, 2013) and macrorestriction patterns were analyzed using the BioNumerics 7.6 (Applied Maths, Kortrijk, Belgium). Results: Results are based on 1772 environmental samples tested, 135 (7.6%) samples were found positive for Listeria monocytogenes (94 NFCS and 41 FCS) in 4 DP and 6 MP. PFGE showed indistinguishable persistent strains in 2 DP and 3 MP in all sampling sessions and in one MP in 3 sampling sessions. Conclusion: The persistence of Listeria monocytogenes underlines the ability to persist in food producing plants, in favourable niches inside the processing environment. To reduce Listeria monocytogenes prevalence, Good Manufacturing Practices and Good Hygiene Practices are needed. Analysis are still ongoing to model the contamination path, NGS on isolated strains will be carried out to confirm the persistence of the strains and to find the presence of gene devoted to resistance and persistence.