A whole genome-based characterization of Listeria monocytogenes strains isolated from invasive infections in Northwest Italy, 2022-2025.

INTRODUCTION

Listeria monocytogenes is a primary foodborne pathogen and the causative agent of human listeriosis and remains one of the most critical foodborne pathogens responsible for severe invasive infections with high hospitalization and mortality rates. According to the European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC), listeriosis continues to show a stable trend, particularly among elderly and immuno-compromised populations. The integrations of Whole Genome Sequencing (WGS) data into routine surveillance represent a key advancement in food safety monitoring and rapid detection and resolution of outbreaks. Since March 2022, the Regional Reference Centre for Salmonella Typing (CeRTiS) has implemented WGS as a standard typing tool for the public health surveillance of L. monocytogenes.

METHODS

This study presents WGS-derived data characterizing 135 L. monocytogenes strains collected from human cases in Northwest Italy between 2022 and 2025.

RESULTS

High-resolution typing based on cgMLST and phylogenomic analysis identified 36 sequence types grouped into 29 clonal complexes (CCs). The most prevalent were: CC1 (20.7%), CC3 (13.3%), CC155 (10.3%), CC8 (7.4%), and CC6 (5.2%).

DISCUSSION: The predominance of Lineage I complexes, specifically CC1 and CC3, which are traditionally associated with invasive clinical disease indicates the persistent circulation of hypervirulent clones. Furthermore, the detection of ST155, recently linked to multinational clusters reported by the ECDC, highlights the necessity of supranational genomic surveillance in tracking the spread of potential epidemic lineages. This study reinforces the role of genomic epidemiology as a cornerstone of modern One Health strategies for preventing and controlling listeriosis.