Evaluation of in vitro growth-inhibitory interactions between essential oils and their volatile compounds against Staphylococcus aureus in vapour phase.

Ing. Marie Straková

Disertační práce

Abstract:

Due to the quick acquisition of drug resistance, Staphylococcus aureus is one of the most serious human pathogens. Nowadays, this bacterium is resistant to almost all antibiotics used. One of the strategies for successful treatment of infections caused by resistant microorganisms is the use of drug combinations. With the aim to develop a proof-of-concept approach that could be used in development of novel preparations for inhalation therapy that would be based on interactions between plant volatile agents [essential oils (EOs) and their constituents], we designed a new broth volatilization chequerboard method for in vitro determination of antimicrobial combinatory potential of plant volatiles simultaneously in liquid and vapour phases. The method is based on combination of standard chequerboard and new broth microdilution volatilization test, allowing calculation of fractional inhibitory concentration (FIC) values. The practical usability and accuracy of the novel technique was verified on three different combinations of plant volatile agents: 1) two plant-derived volatile compounds (carvacrol and thymol), 2) compound (8-hydroxyquinoline) and EO (Cinnamomum cassia EO), and 3) two EOs (Origanum vulgare and Thymus vulgaris EOs), which were tested against standard strains and clinical isolates of S. aureus. Results of all three tested interactions showed to produce additive antimicrobial effects against all tested strains in both phases. In several cases, they reached ΣFIC values lower than 0.6, which can be considered as a strong additive interaction. The most effective interactions in the vapour phase were observed against standard strain of S. aureus ATCC 25923 (ΣFIC = 0.51) when tested carvacrol and thymol, against a clinical isolate (ΣFIC = 0.56), when tested 8-hydroxyquinoline and C. cassia interactions, and against standard strain ATCC 29213 (ΣFIC = 0.59) when tested O. vulgare and T. vulgaris EOs. Using dual-column/dual-detector system for gas chromatography/mass spectrometry analysis of EOs, (E)-cinnamaldehyde was identified as the main constituent of C. cassia bark, while volatile oils from O. vulgare and T. vulgaris aerial parts consisted predominantly of carvacrol and thymol, respectively. The results show validity of our new broth volatilization chequerboard method, which allows cost and labour effective high-throughput antimicrobial screening of interactions between volatile agents with no need of special apparatus. These results can be potentially applied in development of various pharmaceutical applications that are based on volatile microbials and can be used through inhalation therapy against respiratory infections caused by S. aureus. However, further research focusing on in vivo evaluation will be necessary before its possible practical use.

Keywords

antimicrobial interactions, broth volatilization chequerboard method, chemical composition, fractional inhibitory concentration, GC/MS analysis, respiratory infections, synergy

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 19. 1. 2022

Obhajoba závěrečné práce

• Vedoucí: prof. Ing. Ladislav Kokoška, Ph.D.
• Oponent: Pavel Klouček, doc. Ing., Ph.D., Pavlína Kyjaková, externi, Jakub Mrázek, Ing., externi

Česká zemědělská univerzita v Praze

Fakulta tropického zemědělství

Doktorský studijní program / obor:
Zemědělská specializace / Tropical Agrobiology and Bioresource Management