Comparative analysis of 16S and 23S rRNA sequences of Listeria species.

In order to establish the taxonomic value of 16S rRNA and 23S rRNA for distinguishing Listeria species, the complete 23S rRNA sequences for all Listeria species were determined by using the type strains. We designed and experimentally validated a universal 23S rRNA sequencing method, which included PCR amplification of the rDNA gene and direct cycle sequencing of the amplicon with eubacterial primers. The results of our sequence comparison indicated that the genus Listeria can be divided into two subgroups; one subgroup is composed of Listeria monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, and Listeria welshimeri, whereas the other subgroup includes Listeria grayi subsp. grayi and Listeria grayi subsp. murrayi. A phylogenetic analysis revealed that these species diverged recently. These results are consistent with 16S rRNA sequence analysis data. For application purposes, one 16S rRNA region that can be sued to distinguish each Listeria species except L. Monocytogenes and L. innocua has been described. In this study we found four 23S rRNA signature regions which, when used in combination, can be used to distinguish the species.