Bacteriophage are viruses that attack and destroy bacteria and it may be possible to use them to treat bacterial infections. Multiple-drug resistant bacteria are a major medical problem because they are resistant to so many antibiotics. This makes them very difficult, if not impossible, to eradicate. To make matters worse, the incidence of antibiotic-resistant bacteria is increasing. They don't attack any other life form.
Phage are highly specific for the species and strain of bacteria that they attack.
This specificity could be used to selectively attack disease-causing bacteria, especially when antibiotics fail. It is likely that the use of phage will be limited to intestinal and topical infections. If used systemically, the immune system will respond as it would for a vaccination and attack the phage. However, in the intestine, they can reproduce over an extended period of time providing long lasting protection. Bacteriophage were once considered for use in combating bacterial infections.