Abstract
Listeria monocytogenes has caused numerous human outbreaks. Here we report draft genomes of L. monocytogenes J1816 and J1-220, which belong to epidemic clones II and IV, respectively. Whole-genome sequence analysis of these strains provides a tool for studying the short-term evolution of these epidemic clones.
GENOME ANNOUNCEMENT
Listeria monocytogenes is an intracellular, food-borne pathogen that can cause the sometimes fatal disease listeriosis among high-risk populations (7). Listeriosis outbreaks are usually caused by a small portion of the entire population. Among the 13 serotypes of L. monocytogenes, 4b, 1/2a, and 1/2b have been associated with the vast majority of the outbreaks and sporadic cases (1, 4). Many outbreaks were caused by a small number of outbreak clones of L. monocytogenes, i.e., epidemic clone I (ECI), ECII, ECIII, and ECIV (2). ECI caused several major outbreaks associated with coleslaw (Nova Scotia, 1981), soft cheese (Switzerland, 1983 to 1987; California, 1985), and pork tongue (France, 1992). ECII caused an outbreak associated with hot dogs (U.S. multistate outbreak, 1998 and 1999) and another outbreak associated with turkey deli meat (U.S. multistate outbreak, 2002). ECIII caused a sporadic case associated with a hot dog (United States, 1989) and an outbreak associated with turkey deli meat (United States, 2000). ECV caused an outbreak associated with pate (United Kingdom, 1988), an outbreak associated with vegetables (Boston, MA, 1983), an outbreak associated with milk (Boston, MA, 1983) and an outbreak associated with corn (Italy, 1997) (1, 3, 4, 5). Identification of the genetic relationship among different strains in the same epidemic clone is critical to understanding the short-term spread and evolution of L. monocytogenes. However, strains within an epidemic clone have very similar genetic backgrounds and often cannot be distinguished using various molecular subtyping methods. For example, different ECIII strains were identical by seemingly all molecular subtyping methods, such as ribotyping, pulsed-field gel electrophoresis, and multilocus sequence typing. Whole-genome sequencing was the only tool to identify the genetic difference among different ECIII strains (9).
To date, whole-genome sequences of one ECI strain, one ECII strain, and one ECIV strain have been reported: F2365, involved in the 1985 CA outbreak associated with soft cheese; H7858, involved in the 1998 U.S. outbreak associated with hot dogs (8); and HPB2262, involved in the 1997 Italy outbreak associated with corn (3). In the present publication, we announce the availability of draft genomes of another ECII strain, J1816, involved in the 2002 U.S. outbreak associated with turkey deli meat, and another ECIV strain, J1-220, involved in an outbreak associated with vegetables.
Genomic DNA of each strain was isolated from overnight cultures using the DNeasy Blood & Tissue Kit (Qiagen). The genomes were sequenced using 454 Titanium pyrosequencing (Roche) according to the manufacturer's instructions at 20× coverage. Genomic sequence contigs for strain J1816 were assembled using L. monocytogenes 4b H7858 (accession number AADR00000000) as a reference, and the J1-220 genome was assembled using L. monocytogenes strain 4b F2365 (accession number AE017262) as a reference. Assemblies were performed using the Roche Newbler software version 2.3. The sequences were annotated using the NCBI Prokaryotic Genomes Automatic Annotation Pipeline (http://www.ncbi.nlm.nih.gov/genomes/static/Pipeline.html) (6). A detailed report of a full comparative analysis of the genomes of these strains and other available L. monocytogenes strains will be included in a future publication.
Nucleotide sequence accession numbers.
The draft genome sequences of strains J1816 and J1-220 are available in GenBank under accession numbers AFBU00000000 and AFBV0000000, respectively.
Acknowledgments
The publication was made possible by FDA Foods Program intramural funds.
Footnotes
Published ahead of print on 6 May 2011.
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