Distribution and genetic characterization of Listeria monocytogenes prophages

  Objective   This study aims to investigate the distribution and genomic characteristics of the prophages in Listeria monocytogenes.

  Methods  275 Listeria monocytogenes genomes were selected and used to predict prophages by prophage prediction software (PHASTER). The complete prophages were also subjected to clustering analysis, insertion site identification and prophage integrase polymorphism analysis. In addition, the prophages were searched for possible drug resistance genes and virulence genes carried by comparing the drug resistance gene and virulence gene database.

  Results  In this study, 99.3% of Listeria monocytogenes carried prophages, and 155 strains (56.4%) were predicted to have 229 complete prophages, which were divided into 4 groups and 10 clusters. Prophage groups were correlated with strain lineages, but not with strain origins. Ten prophage insertion sites were identified in this study, among which lmot17(tRNA^Arg), lmot11(tRNA^Ser) and comK were the three most common insertion sites, and lmo1263 was a newly identified insertion site. The amino acid sequences of integrases carried by the prophages in same insertion site had high similarity. In addition, the gene coding for virulence-associated protein E (virE) was found in the prophage of some lineage Ⅲ strains and one lineage Ⅰ strain, and no drug resistance gene was found in all intact prophages.

  Conclusion  Listeria monocytogenes commonly carried prophages, more than half of the strains carrying an intact prophage with a diverse genome and multiple insertion sites in the host bacterium chromosome. These insertion sites are associated with integrase amino acid sequences carried by the prophage. In addition, no antibiotic resistance genes were found in prophages in Listeria monocytogenes.