In this study, a new broth macrodilution volatilization method for the simple and rapid determination of the antibacterial effect of volatile agents simultaneously in the liquid and vapor phase was designed with the aim to assess their therapeutic potential for the development of new inhalation preparations. The antibacterial activity of plant volatiles (β-thujaplicin, thymohydroquinone, thymoquinone) was evaluated against bacteria associated with respiratory infections (Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes) and their cytotoxicity was determined using a modified thiazolyl blue tetrazolium bromide assay against normal lung fibroblasts. Thymohydroquinone and thymoquinone possessed the highest antibacterial activity against H. influenzae, with minimum inhibitory concentrations of 4 and 8 µg/mL in the liquid and vapor phases, respectively. Although all compounds exhibited cytotoxic effects on lung cells, therapeutic indices (TIs) suggested their potential use in the treatment of respiratory infections, which was especially evident for thymohydroquinone (TI > 34.13). The results demonstrate the applicability of the broth macrodilution volatilization assay, which combines the principles of broth microdilution volatilization and standard broth macrodilution methods. This assay enables rapid, simple, cost- and labor-effective screening of volatile compounds and overcomes the limitations of assays currently used for screening of antimicrobial activity in the vapor phase.

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.

The number of individuals affected by dementia and cognitive decline is progressively increasing, becoming a serious global health challenge. Several investigations underline the role of nutrition and dietary habits as a preventive strategy. Recent studies suggest that dietary supplementation with polyphenols may constitute an efficient preventive strategy. Indeed, it is emerging that polyphenols exhibit a neuroprotective effect because of their pronounced antioxidant and anti-inflammatory activity. Notably, several studies underline the role of the gut microbiota in the metabolism of the polyphenols, producing bioactive molecules that are absorbed through the gastrointestinal tract. They may exhibit beneficial effects on the central nervous system. Moreover, dietary polyphenols modulate gut microbiota composition, demonstrating a reciprocal regulation between gut microbiota and polyphenol-induced effects on brain functions. Thus, polyphenols are proposed to have an important role on the gut–microbiota–brain axis regulation. The literature search for this narrative review was conducted across three electronic databases PubMed, Scopus, and Web of Science as well as the NIH ClinicalTrials.gov registry, covering the period from January 2000 to 10 February 2026. The following search terms were used: “polyphenols”, “microbiota”, “gut–brain axis”, “dementia”, “cognitive function”, “polyphenols and cognitive dysfunction”, and “polyphenols and microbiota”. The study selection process was performed in two sequential stages: (i) screening of titles and abstracts, followed by (ii) full-text assessment for eligibility. Articles were included if they were peer-reviewed studies (in vitro, in vivo, or clinical trials), published in English, and addressed the effects of polyphenols on cognitive outcomes, gut microbiota composition, or the gut–microbiota–brain axis. Exclusion criteria included non-peer-reviewed sources, studies lacking relevant cognitive or microbiota-related endpoints, and publications not available in full.

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 growth-inhibitory effect of Indian medicinal plants against pneumonia-causing bacteria in liquid and vapor phase. Among all samples tested, Trachyspermum ammi EO exhibited 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 was found to be non-toxic to normal lung fibroblasts were 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 was 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 thera-peutic potential of Indian medicinal plants in inhalation therapy.

In this study, we describe a newly designed microplate sealing lid (SLIM-V®) and its use for susceptibility testing of vapours of plant-derived volatile agents against pneumonia causing bacteria. The in vitro growth-inhibitory effect of volatile compounds (trans-anethole, 4-isopropyl-3-methylphenol, β-thujaplicin and thymoquinone) and essential oils (EOs) from aerial part of Thymus vulgaris, fruits of Hellwigia musifolia, and leaves of Wurfbainia mindanaensis and two forms of Kolowratia eruciformis with red and white calyces were evaluated against respiratory pathogens in vapour and liquid phase using SLIM-V. As a result, thymoquinone was found to be the most active in both liquid and vapour phase against all pneumonia causing bacteria with MIC values ranging from 16 to 64 µg/mL, followed by β-thujaplicin (MICs 32-1024 µg/mL). GC/MS analysis using two columns of different polarity (HP-5MS/DB-HeavyWAX) showed that β-caryophyllene (49.40/35.85 %), α-pinene (20.68/21.82 %) and p-cymene (38.32/36.23 %), thymol (65.00/65.50 %), and 1,8-cineol (77.66/68.00 %) are predominant compounds of H. musifolia, K. eruciformis red and white forms, T. vulgaris, and W. mindanaensis EOs, respectively. More detailed analysis of K. eruciformis using GC×GC-TOFMS confirmed variances in the chemical composition of EOs of both forms suggesting their chemotaxonomical distinction. Based on the results of antimicrobial assay, thymoquinone can be proposed for further research focused on development of inhalation therapies. The experiments showed that the use of SLIM-V represents a significant advancement in the methodologies assessing antimicrobial activity of volatiles. This innovative laboratory tool is safer, easier to handle, and provide more reproducible and sensitive results than other methods.