Listeria – Duplicate key as a model for bacterial infections

Rod-shaped cells of the bacterium Listeria monocytogenes attaching to a human mast cell.

Listeria live almost everywhere – in puddles, in soil, on plants as well as in animals and human beings. The main requirement is that enough dead organic material is available as a food source. There are different kinds of listeria, but only Listeria monocytogenes is known to be a pathogen for human beings.   The rod-shaped bacteria are very adaptable – if their supply of oxygen is depleted, they make a shift to an anaerobic “mode of operation”. Even though they are most comfortable between 30 and 37 degrees Celsius, they are still capable of reproduction even in the refrigerator, at five to seven degrees Celsius.  And it is in the refrigerator where the highest level of infection risk exists for humans, since listeriosis is commonly caused by contaminated food. Listeria monocytogenes reproduce in packaged meat, fish and milk products and is highly contagious.

Unless the food is highly contaminated Listeriosis develops undetected in most cases in healthy individuals. However, even when bacterial concentrations are low, infections can be dangerous for individuals with a weak immune system, like pregnant women, their unborn children, and infants.
Listeria have developed a trick with which they can re-program cells in the digestive tract in such a way that the cells accept the bacteria, instead of rejecting them. Once they have overcome the intestinal barrier, they are able to disperse throughout the whole body via the bloodstream and lymph. They then attack the liver, break through either the placenta barrier or the blood-brain barrier and can trigger meningitis.

Scientists at the HZI are conducting research on the mechanisms listeria use to generate access into the intestinal cells; the bacteria use internalin as a kind of “duplicate key”. This involves proteins on the surface of the cell, with which Listeria monocytogenes is able to bond intestinal-tract receptors E-Cadherin and C-met This initiates a chain reaction resulting in the penetration of the pathogen into the intestinal cell. Listeria are thus a significant model for conducting research regarding the question how exactly bacteria are able to get access to our cells. It is only after scientists have understood these mechanisms that they will be in a position to search for possibilities for blocking them.

Therapy for listeria

Cells of Listeria monocytogenes (wild type)

In therapy for listeria, the first step of identifying the illness is the biggest problem, since the reactions of the infected organisms are quite differentiated and listeria, initially, do not usually come under suspicion. If the infection is recognised early enough, various antibiotics are available to help the inflicted body. Those are however only capable of killing the free-moving pathogens and not those already inside the host cells. In this regard Listeria monocytogenes is also quite resourceful; it even occupies the scavenger cells of its host, which actually function as an immune defence. Prevention is therefore particularly important for high-risk groups; hygienic handling of food and avoidance of raw products are the safest methods for sidestepping exposure to listeria.

(Manfred Braun)


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  • Mit dem Dietrich in die Zelle - Listeria-Bakterien unterwandern unser Sicherheitssystem
    Eigentlich leben wir mit Listerien in friedlicher Koexistenz, es sei denn, die Bakterien schleusen sich mit ihrem molekularen Dietrich durch unsere Darmwand in die Blutbahn ein. Dann können sie schwere Infektionen auslösen. Wie sie diese ansonsten so robuste Darm-Barriere durchbrechen, erforscht Tobias Reinl. Folgen Sie ihm in den Keller des HZI...

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    Länge 06:15
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