Abstract
Prophages are commonly found in Listeria genomes, potentially enhancing survival or fitness of Listeria spp. Currently, there is still limited information on the distribution of prophages among Listeria isolates of different allelic types and from various sources. In this study, by using mitomycin C induction, prophages were found in 23/144 isolates (16.0%), including 13 L. monocytogenes and 10 Listeria spp. isolates, resulting in 28 and 11 induced phages, respectively. These prophage-carrying isolates (lysogens) were obtained from foods and food-related environments presenting 3 common allelic types (ATs) of L. monocytogenes (lineage I, II and IV), 4 ATs of L. innocua and 1 AT of L. welshimeri. The likelihood of prophage-carrying isolates of L. monocytogenes was 14.4 (95% CI: 4.9–35.4), and 18.5 (95% CI: 4.8–50.2) for Listeria spp. The 39 induced phages were classified into 3 lysis groups by the host range test against 9 major serotypes of L. monocytogenes and 5 species of Listeria. Most phages were host-specific with higher ability to lyse L. monocytogenes serotype 4 than other serotypes. The genome size of phages ranged from 35±2 kb to 50±2 kb and belonged to two common phage families, Myoviridae and Siphoviridae. Restriction analysis classified 19 selected phages into 16 restriction profiles, suggesting highly diverse prophages with at least 16 types. This may contribute to the variation in the genomes of Listeria. Information obtained here provides basic knowledge for further study to understand the overall role of prophages in Listeria, including roles in survival or fitness in foods and food processing environments.
Highlights
Listeria monocytogenes is an important foodborne pathogen that can cause listeriosis-a serious foodborne illness with mortality rate up to 30% [1]
Classification of allelic types based on Listeria partial sigB sequences Overall, a total of 144 L. monocytogenes and Listeria spp. isolates were subjected to partial sigB sequencing analysis to classify them into allelic types (Table 3 and Fig 1)
In the 90 L. monocytogenes isolates used in this study, five allelic types were observed
Summary
Listeria monocytogenes is an important foodborne pathogen that can cause listeriosis-a serious foodborne illness with mortality rate up to 30% [1]. Several new species have been discovered in the past decade, for example, L. marthii from soil [2]; L. fleischmannii and L. weihenstephanensis in cheese and water, respectively [3,4]. Previous studies have reported that various types of foods and food processing environments can be contaminated with Listeria spp., including L. monocytogenes [5,6].
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