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Influence of cationic antibiotics on phase behavior of rough-form lipopolysaccharide
Authors:Satoshi Fukuoka  Isao Karube
Institution:(1) Shikoku National Industrial Research Institute, 2-3-3, Hananomiya-cho, 761 Takamatsu, Japan;(2) Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1, Komaba, 153 Meguro-ku, Japan
Abstract:The rough-form lipopolysaccharide (LPS) interacted with cationic antibiotic polymyxin B and gramicidin S in solution, and showed altered thermotropic phase behavior and viscoelasticity. The phase behavior was measured by differential scanning calorimetry and quartz crystal microbalance (QCM). Addition of polymyxin B of up to 0.5 mg/mL to the 5.0 mg/mL LPS solution increased gel-to-liquid crystalline phase transition enthalpy (ΔH) and raised the transition temperature (tmax). The further addition of polymyxin B reduced the ΔH value. Gramicidin S produced a different effect, whereby a minor addition reduced tmax and ΔH value of the LPS. The LPS film on the platinum electrode of the QCM indicated a downward shift of resonant frequency and an upward shift of resonant resistance when in contact with the antibiotic solution. An interpretation of these variations is that the LPS on the QCM electrode changed not only film weight, but also viscoelasticity owing to contact with the antibiotic solution. The different effects between the antibiotics between polymyxin B and gramicidin S on the LPS are induced by the difference of the governing effect. Polymyxin B interacts with the LPS electrostatically, whereas gramicidin S interacts by hydrophobic moieties.
Keywords:Lipopolysaccharide  antibiotic  DSC  quartz crystal microbalance  LPS-antibiotic interaction
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