Essential oils (EOs) have great potential in inhalation therapy for the treatment of respiratory infections. However, innovative methods for evaluation of antimicrobial activity of their vapors are still needed. The current study reports validation of the broth macrodilution volatilization method for assessment of the antibacterial properties of EOs and shows the growth-inhibitory effect of Indian medicinal plants against pneumonia-causing bacteria in liquid and vapor phase. Among all samples tested, Trachyspermum ammi EO exhibits the strongest antibacterial effect against Haemophilus influenzae, with minimum inhibitory concentrations of 128 and 256 µg/mL in the liquid and vapor phases, respectively. Furthermore, Cyperus scariosus EO is found to be nontoxic to normal lung fibroblasts assessed by modified thiazolyl blue tetrazolium bromide assay. Chemical analysis performed using gas chromatography-mass spectrometry identified α-citral, cyperotundone, and thymol as the main constituents of Cymbopogon citratus, C. scariosus, and T. ammi EOs, respectively. In addition, β-cymene is identified as the major compound of T. ammi EO vapors when analyzed using solid-phase microextraction and gas-tight syringe sampling techniques. This study demonstrates the validity of the broth macrodilution volatilization method for antimicrobial screening of volatile compounds in the vapor phase and suggests the therapeutic potential of Indian medicinal plants in inhalation therapy.

• Klíčová slova
• Cymbopogon citratus, Cyperus scariosus, GC/MS, MTT assay, Trachyspermum ammi, antimicrobial activity, headspace analysis, macrodilution, respiratory infections, vapor phase, volatiles,
• MeSH
• antibakteriální látky chemie   MeSH
• antiinfekční látky * analýza   MeSH
• léčivé rostliny * MeSH
• lidé MeSH
• mikrobiální testy citlivosti MeSH
• oleje prchavé * farmakologie   chemie   MeSH
• plynová chromatografie s hmotnostně spektrometrickou detekcí MeSH
• pneumonie * MeSH
• volatilizace MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• antibakteriální látky MeSH
• antiinfekční látky * MeSH
• oleje prchavé * MeSH

While the inhalation of Thymus vulgaris L. essential oil (EO) is commonly approved for the treatment of mild respiratory infections, there is still a lack of data regarding the antimicrobial activity and chemical composition of its vapours. The antibacterial activity of the three T. vulgaris EOs against respiratory pathogens, including Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pyogenes, was assessed in both liquid and vapour phases using the broth microdilution volatilisation (BMV) method. With the aim of optimising a protocol for the characterisation of EO vapours, their chemical profiles were determined using two headspace sampling techniques coupled with GC/MS: solid-phase microextraction (HS-SPME) and syringe headspace sampling technique (HS-GTS). All EO sample vapours exhibited antibacterial activity with minimum inhibitory concentrations (MIC) ranging from 512 to 1024 μg/mL. According to the sampling technique used, results showed a different distribution of volatile compounds. Notably, thymol was found in lower amounts in the headspace-peak percentage areas below 5.27% (HS-SPME) and 0.60% (HS-GTS)-than in EOs (max. 48.65%), suggesting that its antimicrobial effect is higher in vapour. Furthermore, both headspace sampling techniques were proved to be complementary for the analysis of EO vapours, whereas HS-SPME yielded more accurate qualitative results and HS-GTS proved a better technique for quantitative analysis.

• Klíčová slova
• antimicrobial activity, broth microdilution, headspace analysis, respiratory infections, thyme, vapour phase,
• MeSH
• antibakteriální látky chemie   izolace a purifikace   farmakologie   MeSH
• Haemophilus influenzae účinky léků   MeSH
• mikrobiální testy citlivosti MeSH
• mikroextrakce na pevné fázi * MeSH
• oleje prchavé chemie   izolace a purifikace   farmakologie   MeSH
• plynová chromatografie s hmotnostně spektrometrickou detekcí MeSH
• Staphylococcus aureus účinky léků   MeSH
• Streptococcus pyogenes účinky léků   MeSH
• Thymus (rostlina) chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• antibakteriální látky MeSH
• oleje prchavé MeSH

Combinatory action of antimicrobial agents such as essential oils (EOs) show to be an effective strategy to overcome the problem with increasing antibiotic resistance of microorganisms, including Staphylococcus aureus. The objective of this study was to evaluate in vitro antimicrobial interactions between Origanum vulgare and Thymus vulgaris EOs against various S.aureus strains in both liquid and vapor phases using the broth volatilization checkerboard method. Fractional inhibitory concentrations (FICs) were determined for both liquid and vapor phases, and the composition of EOs was analyzed by gas chromatography-mass spectrometry using dual-column/dual-detector gas chromatograph. Results of oregano and thyme EOs combination showed additive effects against all S. aureus strains in both phases. In several cases, sums of FICs were lower than 0.6, which can be considered a strong additive interaction. The lowest FICs obtained were 0.53 in the liquid phase and 0.59 in the gaseous phase. Chemical analysis showed that both EOs were composed of many compounds, including carvacrol, thymol, γ-terpinene, and p-cymene. This is the first report on oregano and thyme EOs interactions against S. aureus in the vapor phase. It also confirms the accuracy of the broth volatilization checkerboard method for the evaluation of combinatory antimicrobial effects of EOs in the vapor phase.

• Klíčová slova
• GC/MS, antimicrobial interactions, broth volatilization chequerboard method, chemical composition, fractional inhibitory concentration, gaseous phase, oregano, thyme, volatile compound,
• Publikační typ
• časopisecké články MeSH