What to do with body odor problems? What kills the odor causing bacteria?

You can't stop BO. You can't kill all bacteria. Most of them are important for our health so don't blame them for your bad odor. Occasionally bacteria grow out of control and cause odor, then antibiotics are used but most of the time it is poor hygiene. If attention to hygiene does not solve the problem, then look for a medical or dental cause to treat.