University of Pennsylvania researchers have built artificial defensin molecules, the proteins used by white blood cells to punch holes in bacteria and kill them.

These small molecules are electrically attracted to a bacterium’s outer membrane, and fuse with it to make the holes. Bacteria cannot easily evolve resistance to defensins’ physical damage to their complex membranes, unlike antibiotics (where bacteria can evolve resistance through a simple change that blocks or defuses an antibiotic).

Defensins haven’t been deployed in medicine because they are difficult and expensive to produce, and are typically destroyed by the host’s immune system before they can reach an area of infection. The artificial defensin molecule is small enough to not be detected by the immune system.