Identification of Listeria Isolates by Using a Pragmatic Multilocus Phylogenetic Analysis

Species identification of Listeria isolates remained a tedious process still based on culturing methods that, in recent years, have led to the description of many species that are not even part of the genus Listeria. It is advisable to provide new precise techniques since this taxon includes two pathogens that are usually transmitted through the food chain, Listeria monocytogenes and L. ivanovii. The approach, so-called multilocus phylogenetic analysis (MLPA) that uses several concatenated housekeeping gene sequences, provides accurate and affordable classification frameworks to easily identify Listeria species by simple Sanger sequencing. Fragments of seven housekeeping genes (gyrA, cpn60, parE, recA, rpoB, atpA, and gyrB) from 218 strains of all Listeria species currently described were used to build an MLPA of the concatenated sequence, a total of 4375 bp. All isolates subjected to identification were clustered within the species of Listeria sensu stricto, L. monocytogenes, L. innocua, and L. welshimeri, and some reference strains were reclassified as L. ivanovii and L. seeligeri. Housekeeping-gene sequencing has been demonstrated to represent a pragmatic tool that can be firmly considered in food control.