In vitro growth-inhibitory effect of Cambodian essential oils against pneumonia causing bacteria in liquid and vapour phase and their toxicity to lung fibroblasts

Abstract

Essential oils hydrodistilled from seven Cambodian plant species (Alpinia oxymitra, Boesenbergia rotunda, Cinnamomum cambodianum, Citrus lucida, Limnophila aromatica, Rhodamnia dumetorum, and Sindora siamensis) were tested for their in vitro growth-inhibitory effect against pneumonia causing bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus) using the broth microdilution volatilisation method. Additionally, a modified thiazolyl blue tetrazolium bromide assay was performed for evaluation of their cytotoxic activity to human lung cells. All essential oils exposed some antibacterial efficacy; however, only A. oxymitra rhizome oil was active against all bacteria tested. A. oxymitra pericarp oil was found as the most effective antibacterial agent against H. influenzae in liquid and solid medium with the respective lowest minimum inhibitory concentrations of 64 and 32 μg/mL. Due to its high value for 80% inhibitory concentration of proliferation (>512 μg/mL), this essential oil may be considered as safe to human lung cell lines. Using dual-column/dual-detector system GC/MS analysis, β-pinene was identified as the main constituent of A. oxymitra leaves, pericarp and rhizome oils, while volatile oil from A. oxymitra seeds consisted predominantly of shyobunol. The major constituents of B. rotunda, C. lucida, L. aromatica, R. dumetorum, and S. siamensis oils were ocimene, decyl acetate, limonene, caryophyllene epoxide, and β-bourbonene, respectively. 1,8-cineole was the major compound of C. cambodianum bark and leaf essential oils. Based on these results, A. oxymitra pericarp oil can be considered as an effective antibacterial agent with application potential for the development of inhalation therapy against respiratory infections.