In my micro lab last semester, we did a disc diffusion assay against a staph aureus and e. coli. We were allowed to bring in chemicals to see if they inhibited bacterial growth. I tested lemon, tea tree, and thyme essential oils against staph aureus. Results:
Lemon oil: no zone of inhibition
Tea tree oil: 11 mm clear zone
Thyme oil: 25 mm clear zone
Control: peroxide 40mm clear zone
I have often heard the term
clinical aromatherapist mostly in the massage 'journals' (loosely used) so am not sure about credentials.
see
http://www.naha.org/schools_level_one_two.htm but I am not sure about the organization NAHA - I know nothing about it.