Probing the Evolution of Genes Associated With DNA Methylation in Listeria monocytogenes

In the last decade, there have been increased reports of atypical Listeria and the discovery of new species. There are public health concerns that new strains may come with increased pathogenicity. Hence, this study aimed to establish the prevalence, evolutionary lineage and ancestry of a Listeria monocytogenes collection that includes isolates that harbour a unique set of methylase genes. The addition of methyl groups to DNA can interfere with transcription. Allelic-specific lineage analysis and ribotyping with southern hybridization were carried out after which further phylogenetic analysis was performed in silico. Results show that all the methylase strains belonged to Lineage I and were serotypes 4b or 4d. All designated ancestral strains also belonged to Lineage 1. A Listeria monocytogenes plasmid from a serotype 1/2a (Lineage II) contained sequences homologous to that of Lineage I isolates. The methylase nucleotide sequence in the strains studied appears to be highly conserved in Listeria monocytogenes and not yet orthologous among other bacterial genera. It is of epidemiological interest and public benefit if wider or continuous surveillance is carried out to ascertain if these rare strains are linked with increased pathogenesis, food type or geographical region.