The sequences of the genomes of the bacterium responsible for listeriosis, Listeria monocytogenes, and of the non-pathogenic bacterium Listeria innocua, and their comparison, are published in the magazine Science. This work, coordinated by Pascale Cossart and Philippe Glaser of the Institut Pasteur, will allow a better understanding of the virulence of Listeria monocytogenes, and therefore represents a significant development in the research of this bacterium. The projects resulting from it should lead to better tools for monitoring and fighting against this pathogenic agent threatening our health by means of the food trade.
Listeriosis is an infection contracted by ingesting food contaminated by Listeria monocytogenes, which manifests itself in meningitis, meningoenchephalitis, septicimia, abortions, perinatal infections and gastro-entiritis. Fatal in 20 to 30% of cases, it particularly affects naturally immunosuppressed people (pregnant women, the newly-born, old people) or during an illness (cancer, cirrhosis, immunosuppressant treatment, etc.). Several thousands of cases are reported annually worldwide, mainly in Europe and the United States. Listeriosis is usually sporadic (slightly more than 200 cases each year in France). However Listeria monocytogenes can also be the cause of epidemics: in February 2000, the French government started a serious scare throughout Europe involving the withdrawal of cooked pork meats. Thirty-two cases were discovered and seven people died.
The presence of the bacterium is aided by the lengthening of the cold chain (industrial refrigerating warehouse, domestic refrigerators): in fact, as opposed to many bacteria, it still grows between 3 and 5°C and freezing stops its growth but does not destroy it. In France, the foodstuffs in which Listeria monocytogenes is most frequently found are milk products, and in particular soft cheeses, but also cooked pork meats, especially ready-to-eat dishes such as potted meat, pork tongue in jelly, meats and poultry, smoked fish and seafood.
The fact that Listeria monocytogenes can nestle in various foodstuffs makes it a threat not only for consumers, but also for food-processing manufacturers. Listeriosis is an economic problem as well as a health risk, and manufacturers are waiting for better tools to prevent food contamination.
At the Institut Pasteur, Pascale Cossart, head of the Bacteria-Cells Interactions Unit, and Philippe Glaser, joint manager of the Genomic Laboratory for pathogenic Microorganisms, coordinated a European* consortium for the sequencing of the Listeria monocytogenes genome. At the same time, the two teams at the Institut Pasteur embarked upon the sequencing of the genome of a non-pathogenic species: Listeria innocua. This is the first time that the genomic sequences of a pathogenic and a non-pathogenic bacteria of the same bacterian species have been published together. The comparison of these two genomes brings crucial information to researchers: 270 out of 3000 genes of Listeria monocytogenes are absent from Listeria innocua. Their study will allow not only a better definition of the genes responsible for the virulence of the listeriosis agent, but also a better understanding of its huge capacity to adapt to different environments.
With this aim in mind, a major study has been launched in collaboration with the Centre de Référence des Listeria, located in the Institut Pasteur and managed by Paul Martin: this CNR holds a sizeable collection of more than eighty thousand strains of Listeria with different epidemiological origins. Thanks to the knowledge of the genome of the bacterium, the researchers at the Pasteur Institute are currently developing DNA chips that will allow hundreds of strains to be studied simultaneously: strains taken from the environment, strains emanating from food, isolated illness strains. The purpose: to better understand the characteristics of the strains that are most frequently responsible for listeriosis, and more particularly those resulting in epidemics. The DNA chips will also serve to analyse of Listeria in response to various environments. In fact, in better defining the behaviour of Listeria in the environment, the control of eradication of this bacterium in food can be strengthened. New means can especially be developed to limit its growth in foodstuffs or in the factories manufacturing them.
The DNA chips will also allow the means of microbiological monitoring to be automated and refined, which will facilitate swifter interventions in cases of epidemics.
* A post-genomic program for Listeria monocytogenes,
also financed by the European Commission, is underway.
Source: "Comparative Genomics of Listeria species ": Science, October 26, 2001.
1 Laboratoire de Génomique des Microorganismes
Pathogène (Genomic Laboratory for pathogenic Microorganisms), Institut
Pasteur, Paris, France
2 Unité des Interactions Bactéries-Cellules (Bacteria-Cells Interactions Unit), Institut Pasteur, Paris, France
3 Scientific Computer Department, Institut Pasteur, Paris, France
4 Institute for medical Microbiology, Frankfurt, Germany
5 Servicio de Microbiologia, Hospital Ramon y Cajal, Madrid, Spain
6 Unité INSERM U411, Faculté de médecine Necker-Enfants Malades, Paris, France
7 Department of cell Biology and Immunology, GBF, Braunschweig, Germany
8 LION Bioscience AG, Heidelberg, Germany
9 Grupo de Patogenesis Molecular Bacteriana, Faculdad de Veterinaria, Madrid, Spain
10 Scientific Research and Development GmbH, Oberursel, Germany
11 Centro de Biologia Molecular, Universidad Autonoma de Madrid, Spain
12 TBI-Biozentrum, Universität Würzburg, Germany
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