Host range of Listeria prophages induced from lysogenic Listeria isolates from foods and food-related environments in Thailand

Prophages have been shown to be associated with improving the survival and fitness of Listeria spp., especially Listeria monocytogenes-a fatal foodborne pathogen. Bioinformatics has revealed the presence of many prophages in Listeria genomes. However, understanding the distribution of prophages in Listeria isolates is limited to those that have no sequences available on the database. In this study, Mitomycin C induction was used to obtain prophages in free-floating form. Among 236 isolates from various sources, prophages were induced from 13/108 (12%) isolates of L. monocytogenes and 10/128 (7.8%) isolates of Listeria spp. Of 39 induced phages obtained, most phages were originated from foods. Phenotypic characterization was performed by the host range determination against 17 hosts representing 9 major serotypes of L. monocytogenes and 4 other species of Listeria. Induced phages were classified into three groups. The majority of phages (groups A and C) were host-specificphages with the ability to lyse one to seven (<42%) hosts. However, five phages (group B) showed broader host range than phages in other groups, which could lyse 8-10 (47-59%) hosts. Both induced and isolated Listeria phages showed a high ability to lyse strains of L.monocytogenes serotype 4, while the induced phages showed narrow host range compared to the isolated phages. Host range data allows the prediction of particular L. monocytogenes subtypes or Listeria species that could be affected by the induced phages, leading to gene transfer upon phage infection. Information obtained here is useful to understand the diversity and role of prophages in Listeria genomes.