Scientists ID Listeria Code

French scientists have determined the complete genetic code of the killer bacterium Listeria monocytogenes, a discovery that might pave the way toward developing new means of preventing and treating the bug, which can contaminate unpasteurized dairy products.

"Listeria monocytogenes causes several hundreds of cases every year in the industrialized countries, and is therefore both a public health problem, as well as an economic problem for the agro-food business," said officials at Paris-based Insitut Pasteur, the organization conducting the research. "Foods, particularly cheeses and prepared meat products, regularly have to be withdrawn from the market because of contamination by this bacterium."

Between 20% and 30% of listeria cases are fatal, the institute said. The disease tends to affect newborns, pregnant women, immunocompromised individuals and seniors. Diseases resulting from contamination include septicaemia, brain infections and miscarriage.

A consortium of 10 labs and companies began sequencing the listeria genome in 1998.

The discovery "will allow comparative analysis between a pathogenic listeria and a non-pathogenic listeria," institute officials said. "This comparison should identify previously unknown genetic determinants of L. monocytogenes pathogenicity, and will help improve research on the mode of action of known virulence genes.

"An even larger programme of comparative genomic analysis has started in collaboration with the listeria laboratory at Institut Pasteur," they said. "It is expected to establish the characteristics of L. monocytogenes strains responsible for epidemics and lead to the development of new diagnostic tools and molecular typing."

Recently in France, nine people died from listeria and the institute's National Reference Centre for Listeria still is attempting to identify the food responsible for the outbreak.

In 1999, French authorities started enforcement of a European Union edict against unpasteurized dairy products, which stipulates that listeria not be present in any random 25 g product sample.

Four nonpasteurized cheese types were removed from the French marketplace last year, angering the nation's dairy industry, which claims other European nations and the United States are pressuring France into banning nonpasteurized cheeses.

Listeria traces were found in a sample of Groupe Lactalis' camembert last spring, prompting a recall.

Last year, a U.S. listeria scare linked to milk manufactured by Kohler Mix Specialties Inc. prompted a recall of various types of milk, half & half and whipping cream. The White Bear Lake, MN-based company made products for such brands as Land O'Lakes, Becker's, Kemps, Dairy Fresh, Perkin's, Roundy's and Wendy's. Between 300,000 and 400,000 gallons of products were affected.

Also in 1999, Utica, OH-based Velvet Ice Cream Co. Inc. initiated a recall after listeria monocytogenes was discovered in an ice cream pint at a convenience store.

No confirmed cases of serious illness were reported in either domestic incident.

Edited by Gerry Clark