Once upon a time there was a field of research that had been dormant for over a century, well now it has awakened. Approved clinical trials are in dozens, scientific journals are publishing reviews of the state of the art, the first books are coming out, chronicling unexpected individual successes, and even the first inquiries from major publications such as the Economist are popping up.

We talk about the idea of pitting microorganisms against each other to defeat infections that threaten our health. They are called phage therapies, because the task of dealing with diseases of bacterial origin is entrusted to tiny viruses called phages or bacteriophages, which really means “bacteria eaters.”

After the first attempt by French-Canadian microbiologist Fèlix d’Hérelle in 1919, the approach took root in Georgia and Poland where it’s still stadard care, and was widely adopted elsewhere until the 1940s. Why the decline? The discovery of penicillin made phages appear obsolete, and Western medicine turned its back on the treatments in vogue in the Soviet area. What has changed in recent years, then? Antibiotic resistance has become a global emergency, and we finally have the technologies to perfect phage therapies.

The majority of current trials employ “environmental” phages, as found in nature, without genetic modification. However researchers have already begun testing the first phages armed with CRISPR (specifically with Cas3 that shreds DNA instead of making precise cuts at a single location) and their patentability promises to increase their potential appeal to the private sector. A phage cocktail against urinary tract infections and another for opportunistic infections attacking cancer patients are under study.

It is worth remembering that in nature bacterial cells use CRISPR systems to protect themselves from viruses. Arming phages with CRISPR, then, is a reversal of perspective. The arms race that has engaged the microbial world since the dawn of time serves as a warning that pathogenic bacteria will sooner or later become resistant even to phage therapies. But the possibility of genetically modifying phages is seen as a valuable opportunity to expand the moves at our disposal and lengthen the efficacy of future therapies, probably in combination with antibiotics.