[freeflight]

The mutations might be random but not every mutation is fit to survive any given environment. As such only "the fittest bacteria"* with "the best mutations"* survive in the end. So it's not as random as it might appear, it's actually quite focused.

for that given environment

That's why antibiotics should generally be used as conservatively ass possible because overkilling bacteria does nothing but accelerate the evolution of the few surviving into "super bacteria" that much faster by giving them a harsh environment they can adapt to.