Eradicating all the bacteria on the tongue is not the solution for bad breath.

The bacteria on our tongue and in our month have an important protective role. When they are diminished drastically, say by the chronic use of antibiotics, then the mouth can become prey to colonization by Candida, a yeast-like organism that causes moneliasis (candidiasis). Candida are microorganisms that are different from bacteria, and are present in small numbers in many people's mouths, but are usually kept at bay by the bacteria. Candidal diseases are much more complicated to control than bad breath. So the idea is to keep the number and activity of bacteria on the tongue low, but not get rid of them completely.