Identification of a major Listeria monocytogenes outbreak clone linked to soft cheese in Northern Italy \u2013 2009-2011

Ettore Amato,Antonio Parisi,Stephen John Knabel,Pol Huedo,Sara Lomonaco,Virginia Filipello,Maria Gori,Marina Nadia Losio,Mirella Pontello

doi:10.1186/s12879-017-2441-6

Abstract

BackgroundMolecular subtyping and enhanced surveillance in Lombardy region identified a cluster of possibly related listeriosis cases from 2006 to 2010. This cluster grouped 31 isolates that belonged to serotype 1/2a and Sequence Type 38 (ST38) as defined by Multilocus Sequence Typing (MLST).MethodsOur study expanded the previous investigation to include cases from 2011 to 2014 and used Multi-Virulence-Locus Sequence Typing (MVLST) on all ST38 isolates to better understand their epidemiology and possibly identify a common source outbreak.ResultsOut of 306 L. monocytogenes clinical isolates collected, 43 (14.1%) belonged to ST38 with cases occurring in nine out of twelve Lombardy provinces. The ST38 isolates were split by MVLST into two Virulence Types (VTs): VT80 (n = 12) and VT104 (n = 31). VT104 cases were concentrated between 2009 and 2011 in two provinces, Bergamo and Milan. An epidemiologic investigation was performed and in one case, a matching VT104 isolate was retrieved from a soft cheese sample from a patient’s refrigerator.ConclusionsOur findings revealed a major listeriosis outbreak in Northern Italy linked to soft cheese in 2009–2011, which went undetected by local health authorities. Our study shows that integrating subtyping methods with conventional epidemiology can help identify the source of L. monocytogenes outbreak clones.

Highlights

Molecular subtyping and enhanced surveillance in Lombardy region identified a cluster of possibly related listeriosis cases from 2006 to 2010
Listeriosis cases A total of 306 L. monocytogenes clinical isolates were analyzed over a 9-year period (2006–2014): 139 from cases occurring in the years 2006–2010 [7] and 167 from cases occurring between the years 2011 and 2014
VT80 has been found in other cheeses as Protected Designation of Origin (PDO) Taleggio and Gorgonzola cheese, two products that have an overlapping producing area [19, 26]. These findings suggest that this molecular type (VT80, corresponding to Sequence Type 38 (ST38) and ST101, both belonging to clonal complex 101 (CC101)) might be common in dairy production facilities in Italy, those manufacturing cheese

Summary

Introduction

Molecular subtyping and enhanced surveillance in Lombardy region identified a cluster of possibly related listeriosis cases from 2006 to 2010. This cluster grouped 31 isolates that belonged to serotype 1/2a and Sequence Type 38 (ST38) as defined by Multilocus Sequence Typing (MLST). The LabSS collects clinical isolates of L. monocytogenes and carries out serotyping and molecular subtyping with Pulsed-Field Gel Electrophoresis (PFGE) and Multilocus Sequence Typing (MLST). This allowed for the period 2006–2014 to report in Lombardy a mean incidence of 0.56

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