the use of oregano oil will kill every bacteria known on earth....why? because of the mega over dose.
put the same herb in the human body and the stomach/liver, etc. all break it down and uses the minerals/nutrients just like any other herb/plant/food. the question you posed is asked by every student of david christopher's master herbalist class and he bluntly states that plants will not harm your frirndly bacteria...they are simply foods...