Molecular characterization of Listeria monocytogenes strains isolated from food and human sources

Introduction: The aim of the work was the molecular characterization of L. monocytogenes (L.m.) isolated from food and humans in the period 2019-2021. Materials and methods: A total of 67 L.m. isolates have been collected (UNI EN ISO 11290-1: 2017) at the Food Microbiology laboratories of the IZS Palermo from different food matrices with a prevalence of ready-to-eat food products such as dairy, fresh cheese, meat, fish sampled by Veterinary Services. The bacterial isolates were stored at -20 ° C in Microbank and sent to the LNR of Teramo for the determination of the serogroup (PCR-Multiplex) and molecular investigation (MLST and Whole Genome Sequencing -WGS). The sequencing was carried out on the Illumina NextSeq 500 platform and the data analysis was performed on a bioinformatics and data collection platform of the LNR L.m, called GenPat. N. 39 clinical strains of L.m. were collected at Palermo hospital laboratories (Regional Reference Laboratory for listeriosis). The strains, together with the sheets for the collection of epidemiological data, were sent to the Istituto Superiore di Sanità (ISS- Operational Microbiological Contact Point for L.m.) for molecular characterization by WGS. The sequencing was carried out on an IonTorrent S5 platform and the analysis was performed automatically on a bioinformatics and data collection platform, called IRIDA-ARIES. Results: The results on the molecular characterization of the strains isolated from food showed a prevalence of serogroup IVb (70%), followed by IIa (24%), IIb (4.5%) and IIc (1.5%). The 46.3% of the strains, all belonging to serogroup IVb, have been isolated from milk products (mozzarella and string cheese) taken from the same producer during official controls, in the period August- September 2020, following a positivity detected in self-control. The results of the sequencing carried out by the LNR highlighted the existence of clusters of strains belonging to Clonal Complex (CC) 2, CC199 and CC1. In particular, all the strains isolated in the same cheese ...