*Article* **Antimicrobial Activity of Chamomile Essential Oil: E**ff**ect of Di**ff**erent Formulations**

**Sourav Das 1,4,**†**, Barbara Horváth 2,**†**, Silvija Šafranko 3, Stela Joki´c 3, Aleksandar Széchenyi <sup>2</sup> and Tamás K˝oszegi 1,4,\***


#### Academic Editor: Igor Jerkovi´c

Received: 31 October 2019; Accepted: 21 November 2019; Published: 26 November 2019

**Abstract:** Essential oils (EOs) are highly lipophilic, which makes the measurement of their biological action difficult in an aqueous environment. We formulated a Pickering nanoemulsion of chamomile EO (CPe). Surface-modified Stöber silica nanoparticles (20 nm) were prepared and used as a stabilizing agent of CPe. The antimicrobial activity of CPe was compared with that of emulsion stabilized with Tween 80 (CT80) and ethanolic solution (CEt). The antimicrobial effects were assessed by their minimum inhibitory concentration (MIC90) and minimum effective (MEC10) concentrations. Besides growth inhibition (CFU/mL), the metabolic activity and viability of Gram-positive and Gram-negative bacteria as well as *Candida* species, in addition to the generation of oxygen free radical species (ROS), were studied. We followed the killing activity of CPe and analyzed the efficiency of the EO delivery for examined formulations by using unilamellar liposomes as a cellular model. CPe showed significantly higher antibacterial and antifungal activities than CT80 and CEt. Chamomile EOs generated superoxide anion and peroxide related oxidative stress which might be the major mode of action of Ch essential oil. We could also demonstrate that CPe was the most effective in donation of the active EO components when compared with CT80 and CEt. Our data suggest that CPe formulation is useful in the fight against microbial infections.

**Keywords:** chamomile essential oil; Pickering emulsion; antimicrobial activity; free radical generation
