Genetic diversity of human strains of Listeria monocytogenes in the Czech Republic in 2016-2020.

Study aim: To determine the genetic diversity of human isolates of Listeria monocytogenes obtained in 2016-2020 from clinical laboratories in various locations of the Czech Republic with a focus on their possible epidemic links and virulence using whole genome sequencing data.

Methods: A total of 102 human L. monocytogenes isolates, serotyped by slide agglutination in combination with multiplex PCR serotyping, were used in this study. Whole genome sequencing was performed retrospectively, and based on the obtained data, the clonal relatedness of the tested strains and the presence of virulence genes were assessed using the Ridom SeqSphere+ software.

Results: In 2016-2020, 102 human isolates of L. monocytogenes were characterized, which represented 65% of all cases of listeriosis reported to the ISIN/EPIDAT systems in the Czech Republic in the monitored period. Serotype 1/2a (57%) was dominant, followed by serotype 4b (30%). Strains of serotype 1/2b (12%) and 1/2c (1%) were rarely detected. Based on the analysis of whole genome sequencing data, the strains were assigned to 26 clonal complexes and 27 sequence types. The cgMLST (core genome Multi-Locus Sequence Typing) analysis revealed four clusters of more than three strains, showing high relatedness (differences up to 10 alleles) with a possible epidemic link. The presence of all key virulence genes was confirmed in all strains. Only three strains (of serotypes 1/2a, 1/2b, and 1/2c) carried a point mutation in the inlA gene responsible for the expression of truncated internalin A protein, which is involved in the mechanism of intestinal barrier crossing by L. monocytogenes.

Conclusion: Molecular epidemiology based on whole genome sequencing is an effective tool to study the population structure of L. monocytogenes strains. This study found high heterogeneity of human L. monocytogenes strains, especially for serotype 1/2a, dominant in the Czech Republic. Several clusters with a possible epidemic link have been identified, and their occurrence will be further monitored.