Abstract
Essential oils (EOs) are becoming increasingly popular in medical applications because of their antimicrobial effect. Direct bioautography (DB) combined with thin layer chromatography (TLC) is a screening method for the detection of antimicrobial compounds in plant extracts, for example, in EOs. Due to their lipophilic character, the common microbiological assays (etc. disk diffusion) could not provide reliable results. The aim of this study was the evaluation of antibacterial and anti-biofilm properties of the EO of cinnamon bark, clove, peppermint, thyme, and their main components against Haemophilus influenzae and H. parainfluenzae. Oil in water (O/W) type Pickering nano-emulsions stabilized with silica nanoparticles from each oil were prepared to increase their water-solubility. Samples with Tween80 surfactant and absolute ethanol were also used. Results showed that H. influenzae was more sensitive to the EOs than H. parainfluenzae (except for cinnamon bark oil). In thin layer chromatography-direct bioautography (TLC-DB) the ethanolic solutions of thyme oil presented the best activity against H. influenzae, while cinnamon oil was the most active against H. parainfluenzae. Pickering nano-emulsion of cinnamon oil inhibited the biofilm formation of H. parainfluenzae (76.35%) more efficiently than samples with Tween80 surfactant or absolute ethanol. In conclusion, Pickering nano-emulsion of EOs could inhibit the biofilm production effectively.
Highlights
Essential oils (EOs) have been widely used for antimicrobial, medicinal and cosmetic purposes.In the European Union, these plant extracts can be found in foods, perfumes and pharmaceuticals [1,2]
We can say that the nanotechnological formulation of EOs seem to be a promising solution in anti-biofilm tests, because the Pickering-emulsion without EO has not antibacterial effect, but the Pickering-emulsion with EO resulted decreasing of the biofilm biomass
We suppose that the enhanced biofilm inhibition properties of the Pickering nano-emulsion of EOs may be attributed to the adsorption of silica nanoparticles on the surface and pores of agar membrane or biofilm
Summary
Essential oils (EOs) have been widely used for antimicrobial, medicinal and cosmetic purposes. In the European Union, these plant extracts can be found in foods (as flavorings), perfumes (as fragrances) and pharmaceuticals (as active ingredients) [1,2]. The significance of the EOs and their components as antimicrobial substances are increasing, due to antibiotic-resistant pathogens [3,4]. EOs may represent the richest available reservoir of novel therapeutics [5]. The reliability of the common antimicrobial assays used for EOs is questionable because of their non-water soluble property [6]. Direct bioautography (DB) combined with thin layer chromatography (TLC) is a rapid and sensitive screening method for the detection of antimicrobial compounds. Test microorganism is capable of growing directly on the TLC plate, so each step of the assay is performed on the sorbent
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