Antimicrobial, antibiofilm and biochemichal properties of Thymus vulgaris essential oil against clinical isolates of opportunistic infections

Abstract

Thyme belongs to a genus encompassing over 215 species of hardy perennial herbaceous plants and sub-shrubs, which are native to Europe, particularly around the Mediterranean. Thymus vulgaris L., or garden thyme, with narrow small leaves and clusters of tubular mauve flowers, is used mainly in cookery. Dried herb yields 1% and more essential oil, which is a pale yellowish-red liquid with a sweet, very aromatic odour. Thyme is widely used in the pharmaceutical industry and is a source of substances of antimicrobial effect upon antibiotic-resistant strains of microorganisms. The purpose of our work was to identify the biochemical and antimicrobial peculiarities of Th. vulgaris essential oil against clinical isolates of opportunistic microorganisms. The analysis of thyme essential oil was carried out using GC/MS analysis. The clinical isolates were isolated with the use of differentially diagnostic nutrient media. The antibiotic susceptibility was identified with the help of the disc-diffusion test. The sensitivity of microorganisms to plant extracts was determined by the agar diffusion test. The antibiofilm activity of the extracts was tested in standard 96-well microtitration plates. The GC/MS results confirm the earlier reports that the major volatile constituents obtained from the aerial parts of thyme species were thymol, γ-terpinene, p-cymene, 3-carene and carvacrol. After subjecting the selected essential oil to effective steam distillation, substantial contents of phenolic monoterpenoids were obtained – thymol (67.7%) and γ-terpinene (8.2%). The European Pharmacopoeia set quality standards for thyme essential oil, which dealt mainly with the % content (w/w) of the volatile phenols (expressed as thymol: 36.0–55.0%). Garden thyme essential oil has been found to show a high antimicrobial activity against antibiotic-resistant microorganism strains. The obtained results proved the wide spectrum of antibiotic activity of thyme essential oil. The highest antimicrobial activity was registered against the typical and clinic strains of S. aureus and microscopic Candida genus fungi. Garden thyme essential oil was ascertained to show high antibiofilm-forming activity against S. aureus. The antimicrobial and antibiofilm-forming activities of thyme essential oil against both bacterial pathogens of opportunistic infections and microscopic fungi have proven the good prospects for development of a broad-spectrum agent against opportunistic microbial associations based on this oil.

Keywords

• antimicrobial effect; antibiofilm formation; essential oil; garden thyme, large-scale distillation.