I’ve always been under the impression that as long as the toothbrush is allowed to dry completely, that takes care of any bacteria. If you’re really concerned about germs on your toothbrush, soaking it in Listerine is an easy way to disinfect it, as @lillycoyote said, or you could get one of those UV germ-killing toothbrush holders.
If you are really concerned about germs on your toothbrush, don’t keep it in the bathroom when you’re not using it. Or at the very least, close the toilet lid when you flush. What’s coming from your mouth is the least of your worries in terms of germs. :)