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. 2023 May 24;23(1):168.
doi: 10.1186/s12906-023-03966-1.

Flowering phenophases influence the antibacterial and anti-biofilm effects of Thymus vulgaris L. essential oil

Csongor Bakó #  1 , Viktória Lilla Balázs #  1 , Erika Kerekes  2 , Béla Kocsis  3 , Dávid U Nagy  4 , Péter Szabó  5 , Giuseppe Micalizzi  6 , Luigi Mondello  6   7   8 , Judit Krisch  9 , Dóra Pethő  10 , Györgyi Horváth  11
Affiliations

Flowering phenophases influence the antibacterial and anti-biofilm effects of Thymus vulgaris L. essential oil

Csongor Bakó et al. BMC Complement Med Ther. .

Abstract

Background: Essential oils are becoming increasingly popular in medicinal applications because of their antimicrobial effect. Thymus vulgaris L. (Lamiaceae) is a well-known and widely cultivated medicinal plant, which is used as a remedy for cold, cough and gastrointestinal symptoms. Essential oil content of thyme is responsible for its antimicrobial activity, however, it has been reported that the chemical composition of essential oils influences its biological activity. In order to explore flowering phenophases influence on the chemical composition of thyme essential oil and its antibacterial and anti-biofilm activity, plant materials were collected at the beginning of flowering, in full bloom and at the end of flowering periods in 2019.

Methods: Essential oils from fresh and dried plant materials were distilled and analyzed with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID). The antibacterial activity was performed by broth microdilution and thin layer chromatography-direct bioautography (TLC-DB) assays and the anti-biofilm effect by crystal violet assay, respectively. Scanning electron microscopy was applied to illustrate the cellular changes of bacterial cells after essential oil treatment.

Results: Thymol (52.33-62.46%) was the main component in the thyme essential oils. Thyme oil distilled from fresh plant material and collected at the beginning of flowering period exerted the highest antibacterial and anti-biofilm activity against Haemophilus influenzae, H. parainfluenzae and Pseudomonas aeruginosa.

Conclusion: The different flowering periods of Thymus vulgaris influence the antibacterial and anti-biofilm activity of its essential oils, therefore, the collection time has to be taken into consideration and not only the full bloom, but the beginning of flowering period may provide biological active thyme essential oil.

Keywords: Anti-biofilm effect; Phenophase; SEM; TLC-DB; Thyme essential oil; Thymol; Thymus vulgaris.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Antibacterial activity of TEOs with TLC-DB (without TLC separation)
Fig. 2
Fig. 2
Antibacterial components in the TEOs distilled from fresh plant material after TLC-DB associated with chromatographic separation. Mobile phase: toluene-ethyl acetate 95:5 (v/v); 1 µL indicated the applied volumes of the EOs and 0.2 µL for the standard. (A) TLC plate under UV 254 nm, (B) TLC plate after treatment with vanillin-sulfuric acid reagent and documented in visible light, (C) TLC-DB assay: Bioautograms using H. influenzae, (D) TLC-DB assay: Bioautograms using H. parainfluenzae, (E) TLC-DB assay: Bioautograms using P. aeruginosa (bright zones indicate antibacterial effects); T1-TEO distilled from fresh plant material and collected at the beginning of flowering period (200 mg/mL), T2-TEO distilled from fresh plant material and collected in full bloom (200 mg/mL), T3-TEO distilled from fresh plant material and collected at the end of flowering period (200 mg/mL), thym.-thymol standard (20 mg/mL)
Fig. 3
Fig. 3
Biofilm inhibition activity of thyme EOs distilled from fresh plant material and collected at different flowering phenophases
Fig. 4
Fig. 4
Scanning electron microscopic images of P. aeruginosa (A, D), H. influenzae (B, E) and H. parainfluenzae (C, F) biofilms
See this image and copyright information in PMC

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