Yes, we've grappled with the idea of "good bacteria" before, and decided that the concept does indeed exist. Now, we must deal with the idea that we might someday have half-bacteria half-machines running round in our bloodstreams. Researchers at the Ecole Polytechnique de Montreal in Canada have combined live bacteria with microcopic "beads", to create what they lovingly call "nanobots." These nanobots will reach every corner of your body, and will eventually be able to wipe out infections with deadly accuracy.
The bacteria themselves have been carefully chosen--they have magnetic particles within them, which, in nature, help them navigate away from oxygen. The researchers, however, use this trait to guide the bacteria. They use MRI machines to create changing magnetic fields around the bacteria, which means that they can control the direction in which they're going.
This is a good thing, because the last thing you want in your bloodstream is renegade robo-bacteria running willy-nilly. There's also a second advantage. Your immune system would have never encountered these bacteria before, so it'll start attacking the bacteria. If the bacteria were left to their own devices, the immune system will likely kill them off before they've achieved their goal. Since they can be guided to infections, they'll be able to do their deed well before your immune system gobbles them up.
Sacrificing bacteria to save humans. Now that's a concept we don't have to grapple with.
Source: Technology Review