Bacteriophages are bacteria-eating viruses. There are more types of phages on earth than there are grains of sand.
Phages have the potential for many life-saving uses but are still highly experimental and extremely finicky. Dr. Carl Merrill has been studying phages most of his life. He is 80 years old and starting a new career in making phages available medically.
https://www.statnews.com/2018/10/16/phage-therapy-viruses-carl-merril-navy/