Population Genetic Structure of Listeria monocytogenes Strains as Determined by Pulsed-Field Gel Electrophoresis and Multilocus Sequence Typing

Abstract

Listeria monocytogenes is a ubiquitous bacterium that may cause the foodborne illness listeriosis. Only a small amount of data about the population genetic structure of strains isolated from food is available. This study aimed to provide an accurate view of the L. monocytogenes food strain population in France. From 1999 to 2014, 1,894 L. monocytogenes strains were isolated from food at the French National Reference Laboratory for L. monocytogenes and classified according to the five risk food matrices defined by the European Food Safety Authority (EFSA). A total of 396 strains were selected on the basis of different pulsed-field gel electrophoresis (PFGE) clusters, serotypes, and strain origins and typed by multilocus sequence typing (MLST), and the MLST results were supplemented with MLST data available from Institut Pasteur, representing human and additional food strains from France. The distribution of sequence types (STs) was compared between food and clinical strains on a panel of 675 strains. High congruence between PFGE and MLST was found. Out of 73 PFGE clusters, the two most prevalent corresponded to ST9 and ST121. Using original statistical analysis, we demonstrated that (i) there was not a clear association between ST9 and ST121 and the food matrices, (ii) serotype IIc, ST8, and ST4 were associated with meat products, and (iii) ST13 was associated with dairy products. Of the two major STs, ST121 was the ST that included the fewest clinical strains, which might indicate lower virulence. This observation may be directly relevant for refining risk analysis models for the better management of food safety.IMPORTANCE This study showed a very useful backward compatibility between PFGE and MLST for surveillance. The results enabled better understanding of the population structure of L. monocytogenes strains isolated from food and management of the health risks associated with L. monocytogenes food strains. Moreover, this work provided an accurate view of L. monocytogenes strain populations associated with specific food matrices. We clearly showed that some STs were associated with food matrices, such as meat, meat products, and dairy products. We opened the way to source attribution modeling in order to quantify the relative importance of the main food matrices.

Biomarker Tools to Design Clinical Vaccines Determined from a Study of Annual Listeriosis Incidence in Northern Spain

“…The ST87 ST of the Gipuzkoa outbreak in 2014 (5) was detected in Cantabria as well as other regions in northern Spain (10). The most prevalent ST in our clinical isolates of invasive L. monocytogenes was ST1, consistent with previous reports (10, 13, 14, 17, 18), followed by ST219. With the aid of M. Lecuit and M. Maury (Institut Pasteur, Paris, France), we assigned the corresponding clonal complexes (CC) to these STs.…”

“…Reduced immunocompetency of listeriosis patients was recently reported as a major risk factor for fatal outcomes (12). Epidemiologically specific Listeria monocytogenes genotypes show greater virulence, contributing to more human listeriosis cases (13, 14). Despite accumulating epidemiological data on listeriosis (1–14), effective immunological biomarkers are yet to be established that a priori appear to represent valuable tools to prepare clinical vaccines for patients at high risk of listeriosis, which may help to reduce the incidence of infectious disease.…”

Analysis of the Listeria monocytogenes Population Structure among Isolates from 1931 to 2015 in Australia

“…Clinical isolates were significantly over-represented among the CC1 sub-group, in contrast to an under-representation of CC3 isolates among lineage I clinical isolates ( Supplementary Table S2 ). This strong association of CC1 clones with clinical illness has been identified in a recent large study which determined source associations and virulence of L. monocytogenes subpopulations (Maury et al, 2016), and it has been hypothesized that this subgroup may have increased virulence relative to others (Henri et al, 2016). That large study also noted ST121 and ST9 as significantly over-represented in food sources, and although all the six ST121 isolates in this study were similarly of food origin, no significant association of CC9 isolates in this study were observed with respect to clinical or food sources ( Supplementary Table S2 ).…”

Antimicrobial Susceptibility and Multilocus Sequence Typing ofListeria monocytogenesIsolated Over 11 Years from Food, Humans, and the Environment in Italy

“…These two STs have been found in different food categories. The high level of exposure might be the reason of the high contribution to listeriosis cases of these STs (Henri et al, 2016).…”