In the Soviet Union, they used cocktails of bacteriophage in much the same way as broad-spectrum antibiotics are used, whenever it was impractical to identify t

In the Soviet Union, they used cocktails of bacteriophage in much the same way as broad-spectrum antibiotics are used, whenever it was impractical to identify the bacterial strain. Bacteriophage evolve of their own accord, so phage resistance is temporary. Often the bacteriophage strain you need already exists and you just have to find it. This is much less effort than developing a new antibiotic.