It depends on what your goal is.
If you're trying to create a Superbug, repeated exposure and mass bactericide will eventually develop a possible winner, given enough test subjects and mutations. Sometimes you might hit a local maximum that will always die out. Sometimes the conditions are so extreme that the mutation(s) needed to survive is too far removed. As it is, you don't keep your hands isolated in an ideal temperature-controlled feeding environment. You touch things, you touch your hair, you touch your jeans, this introduces plenty of regular bacteria right back in to the mix.
But if you're aim is sanitation, you should just wash your hands anyway.
Think of it this way, if you kill off 99.9% of bacteria, and only the strongest survives and gets under your skin, your body can and does fight it off, easily, almost offhandedly and you go about your day not even noticing. Your body is complex[citation needed] and it can handle many many small incidents.
The reason you get sick is because your system gets absolutely overwhelmed with an invading force that grows and multiplies out of control.
Every now and then, one of those small incidents spirals in to an uncontrolled disaster, invaders everywhere, multiplying and consuming..... and you get a tummy ache for a few hours!
