MOLECULAR CHARACTERIZATION OF LISTERIA MONOCYTOGENES STRAINS HARBORING LISTERIA INNOCUA PUTATIVE TRANSCRIPTIONAL REGULATOR GENE LIN0464

摘要

The genus Listeria comprises six closely related bacterial species that share considerable morphological, ecological, biochemical and molecular similarities. In this study, through examination of a large collection (n = 84) of Listeria monocytogenes strains, we identified four serovar 4c strains (i.e., RM3894, RM3899, RM3901 and RM3905) that cross-reacted with Listeria innocua putative transcriptional regulator gene lin0464 primers. We then investigated these four unusual strains by polymerase chain reaction (PCR) with primers for several L. monocytogenes species-, virulence- and group-specific genes and a newly identified L. innocua-specific transcriptional regulator lin2455 gene. The fact that the four strains were recognized by L. monocytogenes inlA, lmo0733, inlJ, lmo2672 and lmo1134 primers but undetected by L. innocua-specific lin2455 primers suggests their L. monocytogenes species identity, and this was confirmed by their testing positive for the presence of L. monocytogenes specific rRNA. As these strains displayed a reaction pattern with L. monocytogenes-specific primers that is typical of lineage subgroup IIIA serovar 4c strains (ATCC 19116, RM3030 and FSL-F2-458), they are likely of serovar 4c in the lineage subgroup IIIA in spite of their possession of L. innocua putative transcriptional regulator gene lin0464. It is clear from this and other published examples that the close relatedness of the Listeria species even extends to the occasional possession by one species of gene(s) normally regarded as specific to another species. Given that Listeria species resemble each other closely and often coexist in clinical, food and environmental specimens, it is important to develop a capability to differentiate pathogenic Listeria monocytogenes from nonpathogenic Listeria species, such as Listeria innocua. By employing primers derived from a newly identified L. innocua-specific gene lin2455, along with several L. monocytogenes primers, it is possible to confirm the species and subgroup identity of L. monocytogenes strains (RM3894, RM3899, RM3901 and RM3905) possessing L. innocua putative transcriptional regulator lin0464 gene. From a food safety perspective, the ability to rapidly and precisely determine Listeria food isolates as L. innocua species with polymerase chain reaction targeting lin2455 gene offers a valuable means to verify the nonpathogenic nature of the bacteria present. On the other hand, the benefit of utilizing molecular techniques to distinguish between avirulent serovar 4a and potentially virulent serovar 4c, as well as non4a-non4c (including 7) within lineage III lies in that it will generate additional caution and preparedness among laboratory and hospital personnel in their handling of lineage III isolates that may be potentially pathogenic.