Virginia Filipello

The evolution and epidemiology of Listeria monocytogenes in Europe and the United States.

Listeria monocytogenes is an opportunistic food-borne pathogen responsible for listeriosis, a disease associated with high mortality rates. L. monocytogenes causes invasive syndromes and case-fatality can be as high as 30%, in specific high-risk population groups such as the elderly, immuno-compromised individuals, fetuses and newborns. Acquisition of the disease is mainly due to consumption of contaminated (predominantly ready-to-eat) food. We aimed to provide a state-of-the-art collection of different likely evolutionary models, based on recombination and positive selection, and the phylogenetic relationship between lineages of L. monocytogenes and between them and other Listeria species. We described the most recent findings in comparative pan-genomics, considering the core and accessory genome in relation to virulence and adaptation to different environments. Finally, this review illustrates L. monocytogenes epidemiology and transmission in humans, foods and animals, the surveillance systems of the European Union and United States and the application of molecular techniques as a core tool in epidemiological investigation.

Diversity and persistence of Listeria monocytogenes within the Gorgonzola PDO production chain and comparison with clinical isolates from the same area

Listeria monocytogenes causes invasive syndromes with high fatality rates in specific population groups. Cheeses have been commonly implicated in outbreaks worldwide. Gorgonzola is a cheese only produced in Northwestern Italy (it is the third Italian cheese in terms of production and export) and L. monocytogenes is frequently isolated from the production chain. The aims of this study were to assess the distribution of L. monocytogenes Virulence Types (VTs) in isolates collected in Gorgonzola processing plants and to determine the presence of Epidemic Clones (ECs). Fifty-Six L. monocytogenes strains collected between 2004 and 2016 from cheese and environmental samples were subtyped with Multi-Virulence-Locus Sequence Typing (MVLST) and compared to previously typed strains. Most isolates (n=50) belonged to two new VTs (VT113 and VT114). The remaining isolates belonged to previously identified VTs: VT14-ECVIII (milk chocolate outbreak, 1994, USA) and VT80 (ricotta salata outbreak, 2012, USA). VT14, VT80 and VT113 were shared with isolates from apparently sporadic human cases in the same geographical area and temporal period (Piedmont and Lombardy, 2005-2016). The overall L. monocytogenes population appears to be homogeneous and may be characteristic of Gorgonzola production. Nevertheless, the detection in cheese and environmental samples of VTs observed in clinical isolates or outbreak related strains (VT80, VT14) contributed to better describe the current scenario and pointed out the need for increased surveillance.

Epidemiology and Molecular Typing of Pregnancy-Associated Listeriosis Cases in Lombardy, Italy, over a 10-Year Period (2005–2014)

In developed countries, pregnancy-related listeriosis accounts for 20–43% of total invasive listeriosis. This work describes the first pregnancy-related listeriosis survey in Italy based on two data sources, that is, mandatory notification system and regional laboratory-based network. Out of 610 listeriosis cases reported over a 10-year period, 40 were pregnancy-related (6.6%). Among these, 29 pregnancy-related isolates were available and have been analysed with serotyping, Pulsed-Field Gel Electrophoresis, and Multi-Virulence-Locus Sequence Typing. No maternal fatality was recorded, but 11 (29.7%) pregnancies resulted in a foetal death, a miscarriage, or a birth of a foetus dying immediately after birth. The average incidence of pregnancy-related listeriosis was 4.3 cases per 100000 births, and the proportion of pregnancy-associated listeriosis among ethnic minorities was significantly higher compared to the general population (30.0% versus 3.5%, P < 0.01). L. monocytogenes isolates belonged to serotypes 1/2a, 1/2b, and 4b, with the latter significantly more prevalent among pregnancy-related isolates. Twenty different pulsotypes were distinguished and 16 out of the 29 isolates were classified into seven clusters. A total of 16 virulence types (VTs) were identified. Five VTs accounted for 45% of the total cases and coincided with those of previously described Epidemic Clones (ECs) of L. monocytogenes.

Molecular diversity and antimicrobial susceptibility of Listeria monocytogenes isolates from invasive infections in Poland (1997–2013)

The epidemiology of invasive listeriosis in humans appears to be weakly characterized in Poland, the sixth most populous member state of the European Union. We obtained antimicrobial susceptibility data, PCR-serogroups and genotypic profiles for 344 invasive isolates of Listeria monocytogenes, collected between 1997 and 2013 in Poland. All isolates were susceptible to the 10 tested antimicrobials, except one that was resistant to tetracycline and minocycline and harbored the tet(M), tet(A) and tet(C) genes. Overall, no increasing MIC values were observed during the study period. Four PCR-serogroups were observed: IVb (55.8%), IIa (34.3%), IIb (8.1%) and IIc (1.8%). We identified clonal complexes (CCs) and epidemic clones (ECs) previously involved in outbreaks worldwide, with the most prevalent CCs/ECs being: CC6/ECII (32.6%), CC1/ECI (17.2%), CC8/ECV (6.1%) and CC2/ECIV (5.5%). The present study is the first extensive analysis of Polish L. monocytogenes isolates from invasive infections.

Draft Genome Sequences of 510 Listeria monocytogenes Strains from Food Isolates and Human Listeriosis Cases from Northern Italy

ABSTRACT Listeriosis outbreaks are frequently multistate/multicountry outbreaks, underlining the importance of molecular typing data for several diverse and well-characterized isolates. Large-scale whole-genome sequencing studies on Listeria monocytogenes isolates from non-U.S. locations have been limited. Herein, we describe the draft genome sequences of 510 L. monocytogenes isolates from northern Italy from different sources.