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.