Molecular genetic characteristics of polyresistant Listeria monocytogenes strains and identification of new sequence types
Introduction. Listeria monocytogenes is a causative agent of listeriosis with a lethality rate of up to 21%. The goal is to study the genotypes and phenotypes of 30 L. monocytogenes strains isolated in 8 regions of the Russian Federation in 2015-2018 from people, from food and from waste water. Materials and methods. Susceptibility to antimicrobials for L. monocytogenes strains, serotyping, MLST-typing, whole-genome sequencing, identification of antibiotic resistance genes, virulence genes and stress survival islets genes, and phylogenetic analysis were done. Results. All strains are classified as multidrug-resistant (MDR), resistance genes fosX, pbp-like, lin, norB and sul were identified, their allelic profiles were determined. Sixteen L. monocytogenes sequence types (ST) were identified: four STs belonging to evolutionary line I and twelve STs to evolutionary line II, including 13 previously known STs (ST1, ST2, ST5, ST7, ST9, ST14, ST16, ST20, ST26, ST121, ST155, ST425 and ST451) and three novel STs (ST1453, ST1455 and ST1454). Five serogroups were revealed: 1-2a-3a, 1/2c-3c, 4b, 4a-4c and 1/2b-3b-7. LIPI-1 pathogenicity island (prfA, hly, plcA, plcB, mpl, actA) and LIPI-2 pathogenicity island (inlABCJ) were identified in the genomes of all strains. LIPI-3 pathogenicity island (llsAXGHBYDP) was identified in two strains of the evolutionary line I. SSI-1 and SSI-2 stress survival islets were found in nine and one strains, respectively. Allelic profiles of virulence and stress resistance genes were determined. Phylogenetic analysis revealed a large genetic diversity of the strains. Conclusion. L. monocytogenes MDR strains belonging to widespread and highly virulent sequence types, were identified in the study, three new sequence types were described.