I think to try to get an antibacterial effect from CBD oil you will need to take quite a bit of it.
There was a member Ohyran who was taking 400mg a day and documenting his experiences in this thread:
www.healingwell.com/community/default.aspx?f=30&m=3427199If you use an oil that has similar amount of THC to CBD it greatly increases the antibacterial effect at lower doses compared to CBD only oil.
From my experience low doses of CBD oil are mostly just anti inflammatory.