Could viruses be used as antibiotics?
Could we use viruses that only affect bacteria to act as antibiotics?


Yes. The specific class you're referring to is called a "bacteriophage".

There's quite a bit of research going on surrounding phage therapy as a stand-in or replacement for traditional antibiotics. Here's a Nature Biotechnology article from 2004 that discusses your very topic.

It is practical, carries some risks (mutations being a known and accepted risk), and I wouldn't be surprised to see phages in practice now or sometime soon.