The context is new but we’re familiar with the theory: The enemy of your enemy is your friend.
Using germs to fight germs is the idea behind the Pathogen Predators program of the US Defense Advanced Research Projects Agency (DARPA), which began last May. It’s based on the way bacteria behave in nature. As they compete for resources such as food and living space, bacteria fight a war against each other and have been doing so since their inception – 4 billion years ago. Those that survived have evolved ways of attacking other bacteria. In response, the defenders with stronger protections were favored, and the assailants, in turn, evolved even better weapons, and so on.
Studying that arms race and picking and choosing what may work for us is the focus of the research. For example, Bdellovibrio bacteriovorus, is found in the soil. It attacks prey bacteria by embedding itself between the host’s inner and outer cell membranes, and begins to grow filaments and replicate. The host bacterium eventually explodes and releases more B. bacteriovorus into the environment. In another case, a team has engineered the gut bacterium Escherichia coli to produce peptides that kill Pseudomonas aeruginosa, a microbe that causes pneumonia.
But researchers warn that the enemy of your enemy isn’t always your friend. Some of these predators will attack you too, just as MRSA does. So they have to tease out which ones are toxic to us, and which pathogens (prey) the predators are effective against.
One more thing. From the perspective of bacteria, antibiotics, most of which come from the soil, are simply another front in their battle against one another. We tend to think of ourselves as Lords of the Universe, but when it comes to germ warfare we are relative newcomers dating back mere decades to the advent of the era of antibiotics in the 1940s. In other words, in this war, our ‘enemy’ has had a 4 billion year head start. So by using our know-how to harness theirs, DARPA wants to treat not just battlefield infections, but especially those that are stubbornly resistant to antibiotics – a problem that concerns all of us.