Low genetic diversity and epidemiological significance of Listeria monocytogenes isolated from wild animals in the far east of Russia

The causative agent of listeriosis, a serious disease of humans and animals, Listeria monocytogenes is a ubiquitous bacterium that inhabits both anthropogenic and pristine environments. We report L. monocytogenes isolation from wild animals, humans, food and the environment of a far eastern region of Russia. In total, 654 samples of internal organs of small rodents belonging to the Muridae and Cricetidae families, and 986 samples of the liver and muscles of mollusks and fish were examined to obtain 7 and 14 independent L. monocytogenes isolates, respectively. The wild animal isolates were compared with human (n = 9), food (n = 8) and environmental (n = 3) isolates obtained in the same region. Twenty of the 21 wild animal isolates belonged to the serovar 4b. The serovars 4b, 1/2a, 1/2b, and 4b, 1/2a, 1/2b, 1/2c were found between human and food isolates, respectively. All isolates were characterized into molecular subtypes by DNA sequencing of the 618 bp internal fragment of the house keeping gene prs and 621 bp internal fragment of the virulence gene inlB. Sequence analysis revealed 4 and 13 alleles for prs and inlB fragments, respectively. Distinct prs and inlB alleles clustered into two groups consistently with established phylogenetic lineages. Among isolates of every lineage, the nucleotide diversity of the prs fragment was low; the nucleotide diversity of the inlB fragment was low among wild animal isolates and higher among human isolates. All rodent isolates and 10 of 14 marine organism isolates carried the same allele of the inlB fragment, which was also found among environmental (two of three), food (two of eight) and human (two of nine) isolates.