A synergistic anti-bacterial and anti-adhesion activity of tea tree () and lemon eucalyptus tree ( Hook) essential oils on .

is a Gram-negative bacterial pathogen that colonizes natural and artificial water systems and has the ability to form a biofilm. The biofilm protects from various environmental factors and makes it more resistant to chlorine-based disinfectants. This study investigated the anti-bacterial properties of tea tree ( (Maiden and Betche) Cheel) oil and lemon eucalyptus tree ( Hook) essential oils (EOs) and their synergistic, additive inhibitory and anti-adhesive effects against biofilm formation on polystyrene. The minimum effective concentration (MEC) for tea tree is 12.8 mg ml and for lemon eucalyptus tree EO 6.4 mg ml. In the checkerboard assay, different combinations of these two EO show synergistic and additive anti-microbial activity. The minimum anti-adhesive concentration (MAC) for tea tree is 12.8 mg ml and for lemon eucalyptus tree EO 6.4 mg ml. A combination of 3.2 mg ml tea tree EO and 0.8 mg ml lemon eucalyptus tree EO showed the strongest anti-adhesive effect against on polystyrene. The tested oils and their combination showed intriguing potential to inhibit biofilm formation.