Design of microemulsion formulations loaded Scutellaria salviifolia Benth, Sideritis libanotica Labill. subsp. linearis (Bentham) Bornm, and Ziziphora clinopodioides Lam. extracts from Turkey and in vitro evaluation of their biological activities

: The species belonging to the Lamiaceae family have been useful tools for many years as a folk remedy. In the present study, a microemulsion system was developed with extract of Scutellaria salviifolia Benth (endemic), Sideritis libanotica Labill. subsp. linearis (Bentham) Bornm (endemic), and Ziziphora clinopodioides Lam. Both and related microemulsion formulations were also investigated for their potential biological activities. Pseudo-ternary phase diagrams of formulations were constructed consisting of oil/ mixed surfactant/water emulsion system and a quaternary component. Antioxidant activity was determined by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method. For antimicrobial activity determination, on the other hand, microdilution method was performed with Escherichia coli 25922, Staphylococcus aureus 29213, Candida albicans 14053, and Candida krusei 6258 standard strains. Tested extracts showed S. aureus-specific antibacterial activity with MIC values 64 µg/mL, 256 µg/mL, and 512 µg/mL for S. libanotica subsp. linearis, S. salviifolia, and Z. clinopodioides, respectively. For any other tested strain, considerable antimicrobial activity was not observed (MIC values > 1024 µg/mL). Related formulations were not superior to extracts in terms of antimicrobial activity. All extracts and related formulations appear to have antioxidant activity, and the antioxidant capacity of all formulations is higher than the extracts. When compared to ascorbic acid, formulation of S. libanotica subsp. linearis extract has stronger antioxidant activity. Sideritis libanotica subsp. linearis extract had a remarkable antibacterial activity against S. aureus. It also had a stronger antioxidant capacity than ascorbic acid. Besides, all formulations developed from extracts had antioxidant activity enhancing properties, although they did not contribute to antimicrobial activity. In conclusion, considering the potential antiinflammatory activity due to antioxidant activity, it is predicted that especially the formulation developed with Sideritis libanotica subsp. linearis extract is worth exploring with further studies for topical treatment of S. aureus-infected wounds and burns.