Won't all drugs targeted at microbes fail eventually? Surely they create a strong selective pressure which favours the resistant strains. The wider and more frequently the drug is used the faster this process occurs?
There is some hope though: having a resistant trait is only useful if it helps you survive. Most resistant traits are "costly" to keep around. Thus if we stop using some treatment - completely stop - in 100 years it will likely become useful again as those "microbs" without resistance out compete those with it.