title: The antimicrobial activity of gramicidin A is associated with hydroxyl radical formation.
abstract: Gramicidin A is an antimicrobial peptide that destroys gram-positive bacteria. The bactericidal mechanism of antimicrobial peptides has been linked to membrane permeation and metabolism disruption as well as interruption of DNA and protein functions. However, the exact bacterial killing mechanism of gramicidin A is not clearly understood. In the present study, we examined the antimicrobial activity of gramicidin A on Staphylococcus aureus using biochemical and biophysical methods, including hydroxyl radical and NAD+/NADH cycling assays, atomic force microscopy, and Fourier transform infrared spectroscopy. Gramicidin A induced membrane permeabilization and changed the composition of the membrane. The morphology of Staphylococcus aureus during gramicidin A destruction was divided into four stages: pore formation, water permeability, bacterial flattening, and lysis. Changes in membrane composition included the destruction of membrane lipids, proteins, and carbohydrates. Most interestingly, we demonstrated that gramicidin A not only caused membrane permeabilization but also induced the formation of hydroxyl radicals, which are a possible end product of the transient depletion of NADH from the tricarboxylic acid cycle. The latter may be the main cause of complete Staphylococcus aureus killing. This new finding may provide insight into the underlying bactericidal mechanism of gA.
authors.affiliation: Institute of Biochemistry, Tzu Chi University, Hualien 970, Taiwan.
authors.forename: Je-Wen
authors.initials: JW
authors.lastname: Liou
authors.affiliation: Institute of Biochemistry, Tzu Chi University, Hualien 970, Taiwan.
authors.forename: Yu-Jiun
authors.initials: YJ
authors.lastname: Hung
authors.affiliation: Institute of Medical Sciences, Tzu Chi University, Hualien 970, Taiwan.
authors.forename: Chin-Hao
authors.initials: CH
authors.lastname: Yang
authors.affiliation: Department of Medicine, MacKay Medical College, New Taipei City 252, Taiwan.
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Chen
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D006096:Gramicidin / Q000737:chemistry / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D017550:Spectroscopy, Fourier Transform Infrared; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D006096:Gramicidin; D017665:Hydroxyl Radical