New Aspects Regarding Evolution and Virulence of <i>Listeria monocytogenes</i> Revealed by Comparative Genomics and DNA Arrays

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Listeria monocytogenes</jats:italic> is a food-borne bacterial pathogen that causes a wide spectrum of diseases, such as meningitis, septicemia, abortion, and gastroenteritis, in humans and animals. Among the 13 <jats:italic>L. monocytogenes</jats:italic> serovars described, invasive disease is mostly associated with serovar 4b strains. To investigate the genetic diversity of <jats:italic>L. monocytogenes</jats:italic> strains with different virulence potentials, we partially sequenced an epidemic serovar 4b strain and compared it with the complete sequence of the nonepidemic <jats:italic>L. monocytogenes</jats:italic> EGDe serovar 1/2a strain. We identified an unexpected genetic divergence between the two strains, as about 8% of the sequences were serovar 4b specific. These sequences included seven genes coding for surface proteins, two of which belong to the internalin family, and three genes coding for transcriptional regulators, all of which might be important in different steps of the infectious process. Based on the sequence information, we then characterized the gene content of 113 <jats:italic>Listeria</jats:italic> strains by using a newly designed <jats:italic>Listeria</jats:italic> array containing the “flexible” part of the sequenced <jats:italic>Listeria</jats:italic> genomes. Hybridization results showed that all of the previously identified virulence factors of <jats:italic>L. monocytogenes</jats:italic> were present in the 93 <jats:italic>L. monocytogenes</jats:italic> strains tested. However, distinct patterns of the presence or absence of other genes were identified among the different <jats:italic>L. monocytogenes</jats:italic> serovars and <jats:italic>Listeria</jats:italic> species. These results allow new insights into the evolution of <jats:italic>L. monocytogenes</jats:italic> , suggesting that early divergence of the ancestral <jats:italic>L. monocytogenes</jats:italic> serovar 1/2c strains from the serovar 1/2b strains led to two major phylogenetic lineages, one of them including the serogroup 4 strains, which branched off the serovar 1/2b ancestral lineage, leading (mostly by gene loss) to the species <jats:italic>Listeria innocua</jats:italic> . The identification of 30 <jats:italic>L. monocytogenes</jats:italic> -specific and several serovar-specific marker genes, such as three <jats:italic>L. monocytogenes</jats:italic> serovar 4b-specific surface protein-coding genes, should prove powerful for the rapid tracing of listeriosis outbreaks, but it also represents a fundamental basis for the functional study of virulence differences between <jats:italic>L. monocytogenes</jats:italic> strains. </jats:p>