Microencapsulation of Origanum heracleoticum L. and Thymus vulgaris L. essential oils – Novel strategy to combat multi-resistant Acinetobacter baumannii

Within the global rise of antimicrobial resistance enhanced by the COVID-19 pandemic, where Acinetobacter baumannii has been distinguished as an emerging multi-resistant pathogen, essential oils, become the focus of novel therapeutic approaches. Hypothesizing that encapsulated Origanum heracleoticum L. and Thymus vulgaris L. essential oils could express multi-target approach against A. baumannii, this study aimed to develop microencapsulated systems with optimal technological qualities using 2-hydroxypropyl-β-cyclodextrin as a carrier, and to evaluate their pharmacological potential against A. baumannii, and their morphological and physicochemical characteristics, safety and stability profiles. The highest yield and encapsulation efficiency were obtained with 1:10 essential oil to carrier, and 1.5:10 carrier to water w/w ratios. The formation of inclusion complexes was confirmed by Fourier Transform Infrared Spectroscopy. Both microencapsulates achieved improved homogeneity, particle surface, and thermal stability compared with the pure carrier. Dominant bioactive compounds (carvacrol and p-cymene in O. heracleoticum essential oil, and thymol and p-cymene in T. vulgaris essential oil) remained the most abundant after encapsulation. While non-encapsulated essential oils revealed similar antimicrobial activity towards clinical A. baumannii isolates obtained from COVID-19 patients, encapsulated O. heracleoticum essential oil inhibited the bacterial growth at lower concentrations than T. vulgaris essential oil microencapsulate. All samples significantly reduced the formation of A. baumannii biofilm, for at least 53.90% towards the most infective isolate according to the Caenorhabditis elegans assay. Further, in silico molecular docking study revealed strong interaction pattern of carvacrol and thymol with the outer membrane protein A, which is the main factor for the A. baumannii biofilm formation. Cytotoxicity investigation on human lung A549 cells showed high survival rate in the presence of all tested concentrations, and the stability study revealed notable preservation of the bioactives' content and pharmacological potential. Altogether, microencapsulated essential oils exhibited a multi-target approach towards A. baumannii, with satisfactory preserving capability during storage.