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Listeria genome sequence as basis for improving food safety
By Birgit Hofmann-Reinert

The genome of Listeria monocytogenes, a bacterium linked to outbreaks of food-borne illness, is being sequenced by researchers at The Institute for Genomic Research (TIGR) in Rockville, Maryland, in collaboration with the chief scientific research agency of the US Department of Agriculture (USDA).

The TIGR team began sequencing DNA from the serotype 4b strain of L. monocytogenes in January. "This strain was selected because most food-borne listeriosis outbreaks—and 50 percent of sporadic cases—are caused by strains of this serotype," says Karen E. Nelson, of TIGR, who heads the collaboration with the USDA’s Agricultural Research Agency.

The bacterium Listeria monocytogenes was named in honor of Joseph Lister (1827-1912), an English surgeon, who introduced modern antiseptic surgery.

Using the whole genome shotgun method, the researchers have achieved 8-fold coverage of the genome, which contains about 2.9 million base pairs. The next steps will be to close existing gaps in the assembly and to annotate the genome. Analyses of the complete genome sequence may reveal clues to the bacterium's biology and lead to new strategies for reducing the incidence of food contamination and food-borne illness.

The genome of another strain of L. monocytogenes, EGD-e, was sequenced last year by a consortium of European scientists coordinated by the Institut Pasteur in Paris.

Listeria bacteria are found almost everywhere in the environment, including water and soil. They are best known as contaminants of undercooked meats, raw vegetables, and processed foods such as soft cheeses, and have led to numerous recalls of food. L. monocytogenes causes an estimated 2,500 illnesses and 500 deaths in the United States each year, according to the USDA. Listeriosis is a serious threat for fetuses, newborns, the elderly, and those with weakened immune systems. Infections can be treated with antibiotics, but the disease is fatal in about one third of cases.

See related GNN article
»Genetic code for Listeria bacterium discovered

The Listeria sequence data are currently available through TIGR at

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USDA Research agency sequences genome of food borne pathogen. United States Department of Agriculture, Office of Communications, Washington, DC (June 7, 2001).

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