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Listeria: hunting the culprit using genetic profiling

40/2019, 23.10.2019

Genetic information helps trace the source of foodborne infections

It's a race against time: if food contaminated with germs is in circulation, the source must be found as quickly as possible. The aim is to prevent infections, and even deaths, as far as possible. Methods with which the information from the pathogens' genetic material (genome) can be examined provide important assistance with this. Just how useful they can be is shown by the example of clarifying disease outbreaks caused by listeria. These are potentially pathogenic bacteria found in food. By comparing genetic material information with listeria, it was already possible to find the source of an infection in various cases. "Molecular biological methods and comparing genomic information from food germs are revolutionising the work of the monitoring authorities," says BfR President Professor Dr. Dr. Andreas Hensel. "They are an excellent basis for quickly and clearly locating food contaminated with pathogens."

Tips for protection against listeria can be found at:

The central question in outbreaks is: which pathogen type is responsible for an infection? For example, conventional methods use surface properties, biochemical abnormalities or segments of genetic material information to root out a suspicious microorganism. Although these methods are proven, they cannot determine which genetic variant of the pathogen is involved with absolute accuracy. However, with the emergence of high-resolution methods for genetic material information (high throughput sequencing), it has become possible to drive down to the unique "core" of a germ - the "construction manual" stored in its genes. Since then, whole genome sequencing (WGS) has become increasingly important in detecting pathogenic microbes (https://www.efsa.europa.eu/de/supporting/pub/en-743).

The Study Centre for Genome Sequencing and Analysis was recently founded at the BfR. It serves as a contact partner for the German federal states’ (“Laender”) research laboratories, and provides the National Reference Laboratories located at the Institute with modern "detective methods" for pathogen searches. With this support, the National Reference Laboratories should help to identify risks in a timely manner. The reference laboratories for Listeria monocytogenes (the most dangerous type of listeria), Salmonella, Campylobacter, and Escherichia coli, among others, (https://www.bfr.bund.de/en/reference_laboratories-10485.html) are located at the BfR.

Even if these new methods are groundbreaking, it remains  crucial that health and food monitoring authorities work well together in the future. For example, if there is an outbreak of Listeria monocytogenes in humans, the pathogens isolated by the food monitoring authorities of the federal states ("Laender") will be sent to the BfR. The genetic material will be fully analysed at the National Reference Laboratory. This genome information will then be compared with the genetic material information of listeria that the Robert Koch Institute (RKI) has detected in humans. If the sequence of isolates shows a high degree of relational similarity in the genome, this usually indicates the source of the outbreak. The results of the comparison will be transmitted to the German federal states' ("Laender") monitoring authorities. The mere comparison of the sequence is usually not sufficient to completely clarify an outbreak. There should always be further indicators that plausibly explain transmission. For example, how a product came from the manufacturer to those affected should be documented. With the FoodChain-Lab software, the BfR has developed an effective digital tool for this purpose.

People with a weakened or immature immune system, such as small children, the seriously ill or the elderly, are particularly at risk from listeria. Anyone preparing meals can reduce the risk of transmission by observing kitchen hygiene rules. In order to avoid listeria infections, it is especially important that raw food, such as meat, is adequately heated. Utmost care must also be taken to ensure that no germs are transferred from raw foods (dairy produce, fruit, meat, vegetables) to other ready-to-eat food.

The BfR leaflet "Consumer tips: protection against foodborne infections with listeria" can be found here (in German only):

About the BfR

The German Federal Institute for Risk Assessment (BfR) is a scientifically independent institution within the portfolio of the Federal Ministry of Food and Agriculture (BMEL) in Germany. It advises the Federal Government and Federal Laender on questions of food, chemical and product safety. The BfR conducts its own research on topics that are closely linked to its assessment tasks.

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