Annual report of Laboratoire des Listeria for year 2000

Director : MARTIN Paul (listeria@pasteur.fr)

National Reference Center of Listeria : Laboratory-based surveillance of listeriosis and participation in investigations of listeriosis epidemiology in France.

World Health Organization Collaborating Center for Foodborne Listeriosis : Participation in laboratory-based surveillance of listeriosis in some Countries, multicenter study on L. monocytogenes typing.

Research : characterization of two populations of L. monocytogenes (strains isolated from humans and from foods) by their virulence proteins profiles, development of DNA micro-arrays for typing and epidemiological studies.

National Reference Centre (CNR) 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. The CNR also receives a certain number of strains isolated from foods and their environment during checks carried out by the agrofood industry itself or official controls carried out by veterinary departments 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: (i) to evaluate trends in the total number of cases; (ii) to detect the first clusters of cases at the start of an epidemic; (iii) to follow the progression of listeriosis in populations at risk; (iv) to evaluate the impact of preventive measures on the incidence of the disease; (v) to facilitate the mandatory declaration of the disease (all cases notified to the CNR are immediately transmitted to the health surveillance services) and (vi) to monitor the susceptibility of strains to antibiotics. For strains isolated from food, we are able to monitor the distribution of strains 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.

Situation with respect to human listeriosis in 2000, according to the results of the CNR :

Two hundred and sixteen sporadic cases were registered in 2000, based on the strains received by the CNR. The clinical forms were distributed as follows: 48 (22%) maternal and neonatal forms and 168 (78%) non-maternal and non-neonatal forms. A large decrease in the number of perinatal forms was observed in 1994 and the number of perinatal forms has steadily decreased ever since. The non-perinatal forms were distributed as follows: 110 cases (65%) of bacteraemia/septicaemia, 42 cases (25%) of central nervous system infection and 16 cases (10%) of other forms. This distribution is similar to that observed in 1999.
Between 1996 and 2000, the annual number of cases of listeriosis was between 216 and 230. The results for 2000 therefore confirm the large decrease in the number of cases observed since 1996 (301 cases in 1995). 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 :

participation in the monitoring of listeriosis in certain countries by strain typing,

Collection of information concerning listeriosis in various countries (incidence, epidemiological characteristics),

Multicentre study of typing methods for L. monocytogenes.

Research :

Study of virulence proteins 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 InteractionsBactéries-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. Having compared expression of the virulence genes encoding listeriolysin O (LLO), Act A (involved in actin polymerisation), Ami (bacteriolysin) and InlB (required for entry into host cells) in 300 strains of Listeria monocytogenes isolated from sporadic human cases and 150 strains isolated from foods, attention is currently focused on the gene encoding InlA, which is required for the entry of the bacterium into human intestinal cells.

General approach to the epidemiology of listeriosis.

This programme involves three groups from the Pasteur Institute. Its principal aim is to identify differences between the genomes of L. monocytogenes (a species pathogenic in humans) and L. innocua (a non-pathogenic species) with a view to developing new tools for the epidemiology and typing of Listeria monocytogenes and to improving our understanding of the virulence mechanisms of this species. The laboratory is primarily involved in epidemiological aspects, for the development of a new method of typing for L. monocytogenes based on DNA microarrays.

Publications of the unit on Pasteur's references database

	Office staff	Researchers	Scientific trainees	Other personnel
	Christine PHAN - listeria@pasteur.fr	Paul MARTIN Christine JACQUET Malika GOUALI (chercheur temporaire) Michel DOUMITH (chercheur temporaire)		Laeticia BELLON Evelyne FILIATRE Elodie PINET

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