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uni'wissen 02(4)-2011_ENG

The pathogen that goes by the name pseudo- monas aeruginosa is microscopically small and very dangerous. It is one of the most feared hospital germs, as it is notoriously difficult to treat with antibiotics. However, not only does the bacterium present a threat in hospitals but also in daily life: “Humans can come into contact with the germ in the water, for instance while taking a shower or digging in damp garden soil,” says ju- nior professor Dr. Winfried Römer. Pseudomonas can behave peacefully for an indefinite period of time and then suddenly wreak havoc. The scien- tist is investigating how bacteria invade human cells and cause disease at the Centre for Biologi- cal Signalling Studies (BIOSS) of the University of Freiburg. A weak immune system or damaged skin increase the risk of infection. “Then, in a second wave, the pathogen can cause a second- ary infection that can even lead to death.” The Bacterium Fights Its Way into the Cell In order to determine how the bacterium fights its way into the cell, Römer is studying the com- plex mechanism by which it makes contact with the cell membrane and then works its way inside, for instance into a lung cell. The bacterium first needs a substance it can latch onto, a so-called receptor. “Cell membranes consist primarily of lipids and proteins and are a highly dynamic sys- tem,” says Römer. They are an ideal landing plat- form for pseudomonas aeruginosa. “The initial contact is an interaction between the bacterium’s own lectins – which are sugar-binding proteins – and sugars on the membrane of the cell. This ini- tial contact with the receptor on the cell surface is a weak binding. The pathogen then proceeds to recruit more receptors until an entire cluster of them build a strong binding.” They forms tube- shaped invaginations that reach far into the cell. “Contrary to previous belief, we have been able to Brutal invasion: A bacterium breaks into a defenseless cell. Drawing: Becker 13uni'wissen 04