Antimicrobial Activity of Different Essential Oil Formulations.

The extreme lipophilicity of essential oils (EOs) impedes the measurement of their biological actions in an aqueous environment. We formulated oil in water type Pickering EO nanoemulsions (AEP) with surface-modified Stöber silica nanoparticles (20 nm) as the stabilizing agent. The antimicrobial activity of AEP and its effects on mature biofilms were compared with those of Tween 80 stabilized emulsion (AET) and ethanolic solution (AEE) of the EO. The antimicrobial activity was evaluated by using the minimum inhibitory concentrations (MIC) and minimum effective concentrations (MEC) of the compounds. On planktonic bacterial and fungal cells beside growth inhibition, colony formation (CFU/mL), metabolic activity, viability, intracellular ATP/total protein (ATP/TP), along with reactive oxygen species (ROS) were also studied. EO nanoemulsion (AEP) showed significantly higher antimicrobial activity than AET and AEE. EO nanoemulsions (AEP) generated superoxide anion and peroxides-related oxidative stress, which might be the underlying mode of action of the EO. Unilamellar liposomes, as a cellular model, were used to examine the delivery efficacy of the EO of our tested formulations. We could demonstrate higher effectiveness of AEP in the EO components' donation compared to AET and AEE. Our data suggest the superiority of the AEP formulation against microbial infections.