At least 25,000 people die in Europe every year as a result of multiresistant strains of Staphylococcus aureus. By comparison, about 7,000 people now die of AIDS in Central and Western Europe each year.

Jens Rolff, of Freie Universität, is a researcher working on basic research, observing the immune systems of insects. Compared with the complex processes that take place in the human body, a housefly’s defense mechanisms seem modest at first glance. But they are also highly successful: 80 percent of all living animal species on our planet are insects, and they are older than the first dinosaurs, having existed from the Paleozoic period, 450 million years ago.

One thing is clear to Rolff: Without an effective immune system, insects would have gone extinct long ago. “Unlike vertebrates, whose immune system can adapt to intruders and recall pathogens’ strategies, insects’ bodies always have to respond to foreign organisms and substances all over again,” Rolff says.

A crucial role in the process is evidently played by antimicrobial peptides – protein compounds that have a deadly effect on bacteria, viruses, and fungi. Researchers have already detected and identified hundreds of these compounds in insects. Mammals, like humans, also have this kind of immune protection on their skin and mucous membranes.

In his day-to-day work in the lab, Rolff isolates these insect peptides and brings them together with bacteria: “After two weeks at the most, resistant strains of bacteria form in the petri dish. The individual peptide is no longer very effective against them.” Rolff suspects that the bacteria exchange genes with each other, thereby canceling out the peptide’s effects.

And yet, insects in the wild are hardly ever infected with resistant strains of bacteria. Why? In his studies, Rolff has observed that combinations of different peptides keep the bacteria in check: “The insect’s immune system also constantly changes the composition and dosage of the peptides, and it seems to be highly successful that way.” In this mixture, even peptides that have no effect as isolated proteins are effective in fighting germs. “There seems to be an interaction between the various substances,” Rolff says.

Rolff and his team are the first researchers in the world to take this approach. Rolff is currently working with theoreticians from ETH Zurich to pinpoint the dynamics involved in how the peptides kill the bacteria. The question behind it is whether it is possible to predict, based on these germs’ “mortality statistics,” whether and how resistance will arise. Rolff and his team have already made one important finding: While administering an antibiotic increases the mutation rate in bacteria, the rate does not rise when antimicrobial peptides are used. The implication for humans could be that constantly changing concentrations of different antibiotics could help prevent new resistance. Human clinical trials, at any rate, are now showing that this route is very promising.