Thin film formation by rough form lipopolysaccharide and interaction with cationic antibiotic polymyxin B

A monolayer film of the rough form of lipopolysaccharide (LPS) from Erwinia carotovora at an air-water interface was transferred onto solid substrates to form a multilayer film. The LPS was deposited on hydrophobic graphite as well as on hydrophilic platinum plates. The thickness of the LPS film prepared by a single dipping and removal of the graphite was estimated at 2.7 nm by atomic force microscopy. The repeated dipping of the platinum plate indicated early saturation with reduced subsequent absorption from the pure water subphase, while successive transfers of the LPS were observed from a 2.0 mM MgCl2 solution. The LPS film on the quartz crystal microbalance (QCM) interacted with cationic antibiotic polymyxin B in the solution and exhibited a downward shift of resonant frequency and resistance in proportion to its concentration. The resonant resistance change against the resonant frequency axis was parallel in this interaction. The absorption of the antibiotic on the LPS film prepared in the presence of MgCl2 indicated an increase in mass, but little change in viscoelasticity. A multilayer film of LPS on the QCM was found suitable for subsequent characterizations.