 We are not alone. We carry as many bacteria as human cells in our body. And we need these bacteria because they synthesize precious molecules that we need to survive. At the same time, we are constantly invaded by pathogenic bacteria. And so our immune cells have a really difficult job. They have to function like detectives. They have to find the bad guys. They have to trace them. They have to capture them. And finally, if they are in close proximity, they have to neutralize them. But how much do we really know about the hunting behavior of our immune cells? And how do they go about the hunting? So immune cells can follow very nicely swimming bacteria. And they follow essentially their nose by detecting the chemicals which the bacteria secrete. But then in many real-life scenarios, bacteria do not only swim around in body fluids, but they also firmly adhere to surfaces. And so in order for our immune cells to fight these bacterial infections, it's a lot of mechanical work. It's like a physical fight between the immune cells and the bacteria. So we are very interested in learning more about this physical fight between bacteria and immune cells. In order to do so, we seeded a macrophage in the middle of an infected surface. And you see how this macrophage is clearing out the surface. It's reaching out to bacteria. But at the same time, the bacteria are dividing every 20 minutes. So it's a race between how fast can they digest with respect to the division rates? So how do they hunt? First of all, they have sticky fingers by which they contact bacteria. But usually when they pull via sticky fingers, the forces created are not sufficient to rupture the bacteria off the surface. So guided by the tension between the sticky finger and the body, they protrude their body towards the bacteria. But then they have to cleave, bond by bond, the adhesive bonds between the surfaces. And they do so by pushing the bodies underneath the bacteria, shuffling it up, and then opening a phagocytotic cup that allows to digest the bacteria. So why do we need to know this hunting in such detail? So let me give you an example. If you have urinary tract infection, you will get treated by antibiotics. And urinary tract infections are caused by E. coli. So at that moment, the concentration set to peak level, hopefully high enough to be lethal. But very soon, the concentration drops in your body. The bacteria don't die any longer. But instead, they divide completely normally. And the last point of pinching of the membranes is inhibited. And so they form these long filaments that you see in this video. And we were asking whether filamentation used by antibiotics has an impact on the mechanics. And therefore, in this video, you see how macrophage is fighting a filament. It's attacking this filament for 40 minutes. It completely ignores all the other bacteria right next to it. And after 40 minutes, it retracts. Do we consider this in any of our medical procedure? The answer is no. So ideal would be that we take antibiotics but keep them at a steady high level in order to prevent the filamentation stage. At the same time, E. coli can even survive. A small fraction of E. coli bacteria can survive even inside the macrophage. They are well shielded from antibiotics. And then they can get secreted and live a normal life. And then the entire race starts again. So in order to learn more now, we decided we would like to design a dangling carrot experiment where we dangle a bacterium front of a macrophage and study its hunting behavior. So in order to do that, we take a magnetic bead. And it's addressed up like a bacterium. It's coated with the molecules that you find on a bacterial surface. And then we guide this magnetic bead with a magnetic trap that was designed at Red Nelson's laboratory. And with this magnetic trap, we can either define the position or we can measure the force acting on the bead. And in this video, we try to play with a talk acting on the beak. And it's similar to us playing with a dog and removing the stick out of the mouth of a dog. We try to measure the forces. We try to measure the modes of attack and how a macrophage is really fighting a bacterial infection. And from these and other studies, we hope to learn much more about the detailed hunting behavior of macrophages. We also like to learn more how we can use the mechanical insights into the fights to either understand side effects of the drugs that are currently used or to design new strategies to find bacterial infections, but also other diseases. Thank you very much.