title: Chemical composition, antibacterial activity and related mechanism of the essential oil from the leaves of Juniperus rigida Sieb. et Zucc against Klebsiella pneumoniae.
abstract: BACKGROUND
  Juniperus rigida is used as Tibetan and Mongolian medicine in China for the treatment of rheumatoid arthritis, nephritis, brucellosis and other various inflammatory diseases.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  The essential oil was extracted from the leaves of J. rigida by supercritical CO2fluid 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 α-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±0.25mm) and the lowest MIC and MBC values of 3.125mg/mL. The increase in proteins, 260nm 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 260nm absorbing materials (DNA and RNA). Further phytochemical and pharmacological studies are required for proper scientific validation of the folk use of this plant species.
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: 460724159@qq.com.
authors: Xiaxia
authors: X
authors: Meng
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: dengwuli@163.com.
authors: Dengwu
authors: D
authors: Li
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: danchen26@126.com.
authors: Dan
authors: D
authors: Zhou
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: dmwli@163.com.
authors: Dongmei
authors: D
authors: Wang
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: 756061378@qq.com.
authors: Qiaoxiao
authors: Q
authors: Liu
authors: College of Forestry, Northwest A & F University, Yangling, Shaanxi 712100, China. Electronic address: 1032681957@qq.com.
authors: Sufang
authors: S
authors: Fan
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D008401:Gas Chromatography-Mass Spectrometry; D018653:Juniperus / Q000737:chemistry*; D007711:Klebsiella pneumoniae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D009822:Oils, Volatile / Q000737:chemistry* / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010940:Plant Proteins
keywords: Antibacterial activity; Antibacterial mechanism; Essential oil; Juniperus rigida; Klebsiella pneumonia; caryophyllene (PubChem CID: 5322111); caryophyllene oxide (PubChem CID: 14350); germacrene D (PubChem CID: 5373727); trans-nerolidol (PubChem CID: 5284507); α-caryophyllene (PubChem CID: 5281520)