Diarrhea-related mortality remains an important public health concern, particularly in developing countries, and has become difficult to treat because of antibacterial resistance. The development of synergistic antimicrobial agents appears to be a promising alternative treatment against diar-rheal infections. In this study, the combined effect of tetracycline together with either nitroxoline, sanguinarine, or zinc pyrithione (representing various classes of alkaloid-related compounds) was evaluated in vitro against selected diarrheagenic bacteria (Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Shigella flexneri, Vibrio parahaemolyticus, and Yersinia enterocolitica). The chequerboard method in 96-well microtiter plates was used to determine the sum of the fractional inhibitory concentration indices (FICIs). Three independent experiments were performed per combination, each in triplicate. It was observed that the combinations of tetracycline with either nitroxoline, sanguinarine, or zinc pyrithione produced synergistic effects against most of the pathogenic bacteria tested, with FICI values ranging from 0.086 to 0.5. Tetracycline-nitroxoline combinations produced the greatest synergistic action against S. flexneri at a FICI value of 0.086. Combinations of the agents tested in this study can thus be used for the development of new anti-diarrheal medications. However, studies focusing on their in vivo anti-diarrheal activity and safety are required before any consideration for utilization in human medicine.

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.