Biophysical analysis on destruction of Staphylococcus aureus membrane during Gramicidin A treatment

• Main Authors: Yu-Jiun Hung, 洪郁鈞
• Other Authors: Je-Wen Liou
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/49617079905960444327

碩士 === 慈濟大學 === 醫學研究所 === 97 === Gramicidin A has been recognized as an antibiotic peptide. It was generally believed that Gramicidin A performed its bactericidal ability by forming ion channels on bacterial surfaces. However, the detail mechanism for the bactericidal effect induced by gramicidin A is still not very clear. In this study, we attempted to apply biophysical techniques Fourier transform infrared spectroscopy, Atomic force microscopy and Flow cytometry to investigate the detail mechanism of the Gramicidin A induced bactericidal effect on Staphylococcus aureus surface. According to Fourier transform infrared spectroscopy (FTIR) on Gramicidin A treated bacteria, several peaks corresponding to chemical bonds, such as peptide bonds and phospholipid bilayer polar and apolar group, disappeared during the treatment indicating the disruption membrane proteins and membrane lipids on membrane surface. The atomic force microscope (AFM) images of Gramicidin A treated bacteria indicated that the destruction of the bacteria by the treatment initiated by forming considerably large pores on bacterial surface. Materials in the bacteria then leaked through these large pores and subsequently made the bacteria flat. In final stage, the disrupted bacteria were found to be in dissolved like morphology possibly duo to the total destruction of the bacterial membranes as indicated by the FTIR spectroscopy. As hydroxyl radicals were found to be generated during the treatment according to flow cytometry, the destruction of the bacterial membrane lipids and proteins might be caused by these hydroxyl radicals. This study reveal that during the Gramicidin A treatment on Staphylococcus aureus, apart form the normally believed ion channel formation, the bacteria are more likely be killed also by more complex ways such as large pore formation and reactive oxygen species (ROS) production during Gramicidin A treatment.