P1-62 Diversity of Listeria monocytogenes Isolated from Clinical Cases and Food in Chile

Monday, July 10, 2017
Exhibit Hall (Tampa Convention Center)
Viviana Toledo , Universidad Andrés Bello , Santiago , Chile
Henk Den Bakker , Texas Tech University , Lubbock , TX
Marc Allard , U.S. Food and Drug Administration , College Park , MD
Martin Wiedmann , Cornell University , Ithaca , NY
Helia Bello , Universidad de Concepción , Concepción , Chile
Gerardo Gonzalez-Rocha , Universidad de Concepción , Concepción , Chile
Andrea Moreno Switt , Universidad Andrés Bello , Santiago , Chile
Introduction: Listeria monocytogenes is an important foodborne pathogen that causes severe infections with high mortality rate. This bacterium is ubiquitously distributed in the environment and it can survive and grow in stress conditions as acid, salt, and low temperature; which are conditions usually found in food processing. In addition, a considerable variability in the capacity to cause human infection have been reported for L. monocytogenes lineages. Two listeriosis outbreaks and an increase on listeriosis incidence have been reported in Chile.

Purpose: The aim of this study was to phenotypically and genetically characterize L. monocytogenes isolated from human cases and foods in Chile.

Methods: A total of 37 isolates from different sources were selected for sequencing. Genomes were sequenced with Illumina and reads were assembled de novo using SPAdes. Isolates diversity was assessed with in silico MLST and serotyping. A maximum likelihood phylogenetic tree based on core genome SNPs was conducted. Phenotypic assays on ten isolates included determination of i) cold growth, ii) acid survival, iii) survival on oxidative stress, iv) growth in saline solution, and v) Caco-2 cells invasion. At least three biological replicates were performed and ANOVA test was used for statistical analysis.

Results: The phylogenetic analysis clustered Chilean isolates in two main lineages (I and II). MLST showed that worldwide-distributed clonal groups (CC-1 and CC-9) are also causing clinical cases in Chile. Among the isolates tested large phenotypic assays diversity was observed. No significant differences between lineages were found, except for salt stress assay, in which lineage I isolates showed a better ability to survive at higher concentrations of salt 1.65±0.14 versus 1.52±0.23 CFU/ml from lineage II (P<0.05).

Significance: This study provides baseline data on the genomic and phenotypic diversity of Listeria circulating in Chile and further supports global distribution of key human disease associated L. monocytogenes clonal groups.