Chemical composition, antibacterial activity and related mechanism of the essential oil from the leaves of Juniperus rigida Sieb. et Zucc against Klebsiella pneumoniae

Ethnopharmacological relevance: Juniperus rigida is used as Tibetan and Mongolian medicine in China for the treatment of rheumatoid arthritis, nephritis, brucellosis and other various inflammatory diseases. Aim of the study: To evaluate antibacterial potential of essential oils from J. rigida leaves against Klebsiella pneumoniae and to examine its possible related mechanisms. The study was undertaken in order to scientifically validate the traditional use of J. rigida. Materials and methods: The essential oil was extracted from the leaves of J. rigida by supercritical CO2 fluid extraction technology. Chemical composition of essential oils was analyzed by gas chromatography-mass spectrometry (GC-MS). The antibacterial activity was evaluated against 10 bacteria by the paper disc diffusion method. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of the essential oil were estimated by agar dilution method. The antibacterial mechanism was evaluated by growth curve, the integrity of cell membrane, the SDS-PAGE of protein patterns and scanning electron microscope (SEM). Results: 61 components were identified from the essential oil. Caryophyllene (13.11%) and alpha-Caryophyllene (11.72%) were found to be the major components. The antibacterial activities of the essential oil were screened and compared against 10 bacteria. The essential oil showed good antibacterial activity against K pneumoniae, with the biggest diameters of inhibition zones (DIZ) (16.00 +/- 0.25 mm) and the lowest MIC and MBC values of 3.125 mg/mL. The increase in proteins, 260 nm absorbing materials of bacterial cells suspension indicated that the cytoplasmic membranes were broken by the essential oil. The SDS-PAGE of bacterial proteins demonstrated that the essential oil could damage bacterial cells through the destruction of cellular proteins. Scanning electron microscopy (SEM) showed that the essential oil damaged the morphology of cell wall and membrane. Conclusions: The essential oil of J. rigida has potential antibacterial activities against K. pneumoniae. The antibacterial mechanism is the essential oil causing the irreversible damage to the cell wall and membrane, leading to the leakage of proteins and 260 nm absorbing materials (DNA and RNA). Further phytochemical and pharmacological studies are required for proper scientific validation of the folk use of this plant species.