Liposomal incorporation of Thymus essential oils and in vitro antibacterial activity

Essential oils (EOs) of Thymus species have been known to possess antimicrobial properties and therefore are of great interest in pharmaceutical, food and cosmetic industry. However, they are poorly soluble in water, unstable and susceptible to degradation. Encapsulation of EOs in different nanocarriers represents a valid strategy to overcome these limitations as well as to enhance their biological activity [1], [2]. The present study aimed to evaluate the antibacterial potential of liposomally-encapsulated phenol rich EOs from T. longicaulis C. Presl, T. pulegioides L. and T. vulgaris L. originating from Croatia. The commercial T. vulgaris EO was used for the optimization of liposomes’ composition and preparation procedure. Based on the high encapsulation of EO and satisfied physical properties achieved, liposomes containing 20 mg/mL of soy phosphatidylcholine, 2 mg/mL of cholesterol and 5 mg/mL of EO were selected as optimal for testing the antibacterial activities against S. aureus, E. faecalis and E. coli. The mean diameters of liposomes were 187–216 nm with polydispersity indexes from 0.43 to 0.53, while encapsulation efficiency varied between 51% and 57%. The obtained minimal inhibitory concentrations (MICs) were in the range 0.25–2 mg/mL. Encapsulation of the Thymus EOs in liposomes improved their solubility, stability and enhanced their antibacterial activities exhibiting MICs two-fold lower than the MICs of the corresponding pure EOs against S. aureus and E. coli. Liposomally-encapsulated T. longicaulis EO demonstrated the strongest antibacterial effect showing four-fold increase of activity against E. faecalis, thus indicating its potential use as biopreservative and natural remedy.