Hypo- and Hyper-Virulent Listeria monocytogenes Clones Persisting in Two Different Food Processing Plants of Central Italy.

Fabrizia Guidi,Barbara Palombo,Adriano Di Pasquale,Giuliana Blasi,Romolo Salini,Marina Torresi,Massimo Ancora,Marco Di Domenico,Massimiliano Orsini,Giulia Amagliani,Alexandra Chiaverini,Francesca Romana Massacci,Giorgio Brandi,Patrizia Centorame,Francesco Pomilio,Cesare Cammà,Anna Duranti,Giuditta Fiorella Schiavano,Stefano Fisichella,Vicdalia Aniela Acciari

doi:10.3390/microorganisms9020376

Abstract

A total of 66 Listeria monocytogenes (Lm) isolated from 2013 to 2018 in a small-scale meat processing plant and a dairy facility of Central Italy were studied. Whole Genome Sequencing and bioinformatics analysis were used to assess the genetic relationships between the strains and investigate persistence and virulence abilities. The biofilm forming-ability was assessed in vitro. Cluster analysis grouped the Lm from the meat plant into three main clusters: two of them, both belonging to CC9, persisted for years in the plant and one (CC121) was isolated in the last year of sampling. In the dairy facility, all the strains grouped in a CC2 four-year persistent cluster. All the studied strains carried multidrug efflux-pumps genetic determinants (sugE, mdrl, lde, norM, mepA). CC121 also harbored the Tn6188 specific for tolerance to Benzalkonium Chloride. Only CC9 and CC121 carried a Stress Survival Islet and presented high-level cadmium resistance genes (cadA1C1) carried by different plasmids. They showed a greater biofilm production when compared with CC2. All the CC2 carried a full-length inlA while CC9 and CC121 presented a Premature Stop Codon mutation correlated with less virulence. The hypo-virulent clones CC9 and CC121 appeared the most adapted to food-processing environments; however, even the hyper-virulent clone CC2 warningly persisted for a long time. The identification of the main mechanisms promoting Lm persistence in a specific food processing plant is important to provide recommendations to Food Business Operators (FBOs) in order to remove or reduce resident Lm.

Highlights

Listeria monocytogenes (Lm) is a major foodborne pathogen causing human listeriosis, the most severe zoonoses with the highest hospitalization (97.0%) and fatality (15.6%)rates [1]
In the meat processing plant (Meat A) plant we found strains belonging to CC9, CC121 (IIa) and CC1 (IVb) and both core genome MLST (cgMLST) and Single Nucleotide Polymorphism (SNP) analysis identified three different clusters and four strains clustering outside
Whole Genome Sequencing (WGS) currently provides the highest possible microbial typing resolution and is considered the most practical and relevant laboratory technique to study the full genomes of bacteria

Summary

Introduction

Listeria monocytogenes (Lm) is a major foodborne pathogen causing human listeriosis, the most severe zoonoses with the highest hospitalization (97.0%) and fatality (15.6%). Lm is widespread in the natural environment, animals and food, especially ready-to-eat such as deli meat, dairy products, smoked fish and salads. Once introduced in a food processing facility, several factors increase the probability of a strain to establish long-lasting colonization of niches and to persist [3]. Lm is able to survive and grow under a wide range of environmental conditions, including refrigerating temperatures. Stress resistance genetic determinants have been selected in Lm, conferring resistance to environmental stresses, such as low pH, high osmolarity, bile and nisin

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