Serious bacterial illnesses in countries with good health systems are already pretty rare. The vast majority of them come from unsanitary food practices
If all of our countries with health systems designed for our bacteria aren't equipped to handle more advanced bacteria, wouldn't it take just one explorer to bring back a species-threatening disease?
The space thing is irrelevant. You can't develop pharmaceuticals meant to kill things you don't know anything about
There is no evidence to that. Even the existence of resistant bacteria in agricultural animals doesn't prove there is a danger for Humans.
In Human tuberculosis for example, resistance seems to happen de novo in Humans, normally, after the patients go through multiple ineffective or aborted rounds of treatment.
These therapies are currently very expensive and time consuming, as they require custom testing of libraries of phage against the specific microbial isolate. There have not been any successful large scale clinical trials yet.
For a good review of the field (but behind academic paywall), see [3]
[1] https://aac.asm.org/content/61/10/e00954-17 [2] https://www.nature.com/articles/s41591-019-0437-z [3] https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(1...