Listeria is a rod-shaped bacterium highly prevalent in the environment and generally not a threat to human health. One species however, Listeria monocytogenes, can cause listeriosis, a very dangerous disease. This pathogen can be present in raw milk and soft cheeses, smoked fish, raw meat and ready-to-eat products. In Austria, health care providers are required to report all cases of listeriosis, which can be fatal particularly for patients with weakened immune systems. In 2009 and 2010, a dairy in Hartberg (Styria, Austria) produced Quargel cheese contaminated with Listeria monocytogenes leading to a multinational listeriosis outbreak in Austria, Germany and the Czech Republic, ultimately forcing the dairy to shut down.
Detective work: finding the source
"I'm happy to report that we see relatively few cases of listeriosis here in Austria. When an outbreak occurs though, the disease has among the highest mortality rate of all food-borne illnesses", explains lead author Kathrin Rychli from the Institute for Milk Hygiene, Milk Technology and Food Science at the University of Veterinary Medicine, Vienna. The Institute was involved in investigating the causes of the outbreaks back in 2009 and 2010. The culprits: two distinct bacterial strains which had not recently evolved from a common ancestor, and therefore entered the food chain independently.
Genetics reveal the pathway
In their current study, the scientists sequenced and analysed the genomes of both strains, and assessed their virulence, the ability to infect cells. The samples were taken from listeriosis patients from the outbreak.
The first contamination event from June 2009 to January 2010 was attributed to one L. monocytogenes strain very effective at infecting epithelial cells of the intestine and liver cells. It contained additional four virulence genes, making it extremely invasive, and ultimately ca
|Contact: Dr. Stephan Schmitz-Esser|
University of Veterinary Medicine -- Vienna