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  Director : MARTIN Paul (listeria@pasteur.fr)


  abstract

 

The Listeria Laboratory is homing the National Reference Centre for Listeria and the WHO Collaborating Centre for Food borne Listeriosis. The NRC perform the laboratory-based surveillance of human listeriosis, the detection of epidemics and participate to investigations of listeriosis epidemiology in France. In 2002, the laboratory coordinated the microbiological section of the european project "Feasibility study for a collaborative surveillance of Listeria infections in Europe". The WHO-CC participate to the formation of microbiologists involved in laboratory-based surveillance of listeriosis in their countries and characterize strains of L. monocytogenes from different countries. In research, the laboratory characterize virulence proteins in populations of L. monocytogenes, and develop DNA micro-arrays for typing and epidemiological studies.



  report

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National Reference Centre (NRC) for Listeria.

Listeriosis is a serious disease that preferentially affects subjects with disturbed immune systems (pregnant women and newborns, the elderly, immunocompromised subjects and patients suffering from cancer or cirrhosis or on immunosuppressive treatment). This infection manifests itself in various ways, depending on the case. It may cause abortion or result in the birth of an infected child; it may infect the central nervous system or cause bacteraemia or septicaemia. Diagnosis is based on isolation of the bacterium from a site that is normally sterile. The CNR receives strains isolated by medical biologists and these strains are then characterised by phenotyping and molecular techniques, and participate to the mandatory declaration of the disease (all cases notified to the CNR are immediately transmitted to the health surveillance services). The CNR also receives a certain number of strains isolated from foods and their environment during checks carried out by the agro food industry itself or official controls carried out by the General Directorate for Foods or the laboratories of the General Directorate for Competition, Consumer Affairs and Fraud Prevention.

Regular monitoring of the results makes it possible, for strains of human origin: to evaluate trends in the total number of cases; to detect the clusters of cases; to follow the progression of listeriosis in populations at risk; to evaluate the impact of preventive measures on the incidence of the disease; to monitor the susceptibility of strains to antibiotics. The characterization of strains isolated from food allow the NRC to monitor strain distribution in foods, and to constitute a database to make it easier to identify cases with a food-borne origin among clustered cases.

During epidemics, the CNR fulfils the following functions:

  • Detection of clusters of cases,

  • Identification of epidemic cases,

  • Participation in the identification of the food vehicle responsible, by comparing strains isolated from foods with strains isolated from epidemic cases.

The laboratory coordinate, along with the Institut de Veille Sanitaire, the microbiological section of the european project "Feasibility study for a collaborative surveillance of Listeria infections in Europe".

Situation with respect to human listeriosis in 2001, according to the results of the CNR (data for 2002 will be available by the end of March 2003).

In 2001, 185 sporadic cases were registered, based on the strains received by the CNR. The clinical forms were distributed as follows: 481 (23%) maternal and neonatal forms and 139 (77%) non-maternal and non-neonatal forms. A large decrease in the number of perinatal forms was observed in 1994-96 and the number of perinatal forms has steadily decreased ever since. The non-perinatal forms were distributed as follows: 85 cases (61%) of bacteraemia/septicaemia, 44 cases (32%) of central nervous system infection and 10 cases (7%) of other forms. This distribution is similar to that observed in the previous years.

Between 1996 and 2000, the annual number of cases of listeriosis was between 216 and 230. The year 2001 shows a significant decrease of sporadic cases of listeriosis, when compared with previous years. This decrease must be seen in the light of the measures taken concerning the production and distribution of foodstuffs and the recommendations given to populations at risk.

WHO Collaborating Centre (WHOCC) for food-borne listeriosis

The WHO Centre participate to the technical formation of microbiologists involved in laboratory-based surveillance of listeriosis in their own countries, characterize strains of L. monocytogenes from different countries by typing, and collect informations on listeriosis in different countries.

Research

Study of virulence protein InlA in L. monocytogenes.

Several observations have suggested that certain strains present in food may be less frequently responsible for infections in humans. These observations include the non-uniform distribution of serovars, ribovars, isoenzyme profiles and surface proteins according to whether the strain is of human or food origin. Further evidence that this may be the case is provided by heterogeneity in the virulence of strains in animal and cell models. The work carried out by the "Unité des Interactions Bactéries-Cellules" has demonstrated molecular mechanisms for host invasion in L. monocytogenes. A study of the expression of several virulence factors involved in various stages of the infections cycle is being carried out in collaboration with this unit, to compare clinical strains and strains isolated from food. The expression of protein InlA, required for entry into human intestinal cells, is studied in 300 strains of Listeria monocytogenes isolated from sporadic human cases and 150 strains isolated from foods. A publication is in preparation.

2. Genomic epidemiology of L. monocytogenes.

Partial or total sequences of 3 strains of Listeria (2 L. monocytogenes and 1 L. innocua) allows comparative genomic studies using high density filters, with about 450 ‘specific' gene fragments from each of the studied strains, as a first approach. Genomic DNA from each strain to be tested was hybridised on separate membranes. After acquisition, quantification and normalisation of hybridisation signals, the comparative study is performed a presence/absence basis for each of the 450 tested genes. Preliminary results obtained on about one hundred strains from the collection of the Laboratory of Listeria, of different characteristics and origins, showed a perfect differentiation of Listeria species. More specifically, L. monocytogenes was distributed in 5 different groups, with several subgroups within each. All strains belonging to the same serovar clustered together, and strains from different serovars can regroup in a same cluster group. The screening of genes of potential interest to study the biodiversity of Listeria is in progress. Then, a second line membrane will be designed. This new membrane will be tested on all human strains isolated from sporadic cases in France during the year 2000.

3 -Attenuated strains in natural populations of L. monocytogenes.

This research programme was performed in collaboration with others research groups from the Institute Pasteur, the INRA and the Food Private Industry. It allowed to describe the infrequent circulation of virulence-attenuated strains in natural populations of L. monocytogenes from the Food industry, and to start to characterize such naturally occurring mutants at the molecular level.

Keywords: Listeria, listeriosis, surveillance, virulence proteins



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
  Zoulica LEBRI,listeria@pasteur.fr Paul MARTIN

Christine JACQUET

Marina MACEDO VINAS (temporary fellow)

Michel DOUMITH (post doc fellow)

Loubna HAJOUI (temporary fellow)

  Laeticia BELLON

Evelyne FILIATRE

Elodie PINET

Stephanie DEMAIL

Zina SOUANEF


Activity Reports 2002 - Institut Pasteur
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