Enlarge / See this? This is what we want to avoid. (credit: Cynthia Sears, Johns Hopkins)

Everyone is familiar with it. The buzz of a fly, the thwack as it hits the window, followed by frantic buzzing noises. A fly is stuck against the window, skittering along as it blindly attempts to get through the glass. If only they’d read The Men Who Stare at Goats, they’d realize the futility of their actions. It turns out that bacteria do something similar (and also haven’t done the required reading), but it’s not due to their inability to recognize glass.

Bacteria form films that are, at best, a nuisance, and at worst, downright dangerous. Essentially, if you put a surface into a fluid containing bacteria, they will gather at the surface, possibly swapping stories about the good old minutes long gone. But given enough time, they will often grow into a sticky, cohesive film that covers the surface. On surgical implants and such, this needs to be avoided at all cost.

It’s actually a bit strange that this happens at all. A bacteria that is freely swimming along in water is driven by a great flappy propellor, called a flagella. This thing doesn’t really know where it’s going, so eventually it runs into any walls that you’ve cruelly placed in its path. But this is a tiny object in a fluid, so it is subject to diffusion. In a short time, the forces of diffusion will reorient the bacteria, allowing it to blindly swim away from the surface.