title: Fusion between fluid liposomes and intact bacteria: study of driving parameters and in vitro bactericidal efficacy.
abstract: BACKGROUND
  Pseudomonas aeruginosa represents a good model of antibiotic resistance. These organisms have an outer membrane with a low level of permeability to drugs that is often combined with multidrug efflux pumps, enzymatic inactivation of the drug, or alteration of its molecular target. The acute and growing problem of antibiotic resistance of bacteria to conventional antibiotics made it imperative to develop new liposome formulations for antibiotics, and investigate the fusion between liposome and bacterium.
  
  
  METHODS
  In this study, the factors involved in fluid liposome interaction with bacteria have been investigated. We also demonstrated a mechanism of fusion between liposomes (1,2-dipa lmitoyl-sn-glycero-3-phosphocholine [DPPC]/dimyristoylphosphatidylglycerol [DMPG] 9:1, mol/mol) in a fluid state, and intact bacterial cells, by lipid mixing assay.
  
  
  RESULTS
  The observed fusion process is shown to be mainly dependent on several key factors. Perturbation of liposome fluidity by addition of cholesterol dramatically decreased the degree of fusion with P. aeruginosa from 44% to 5%. It was observed that fusion between fluid liposomes and bacteria and also the bactericidal activities were strongly dependent upon the properties of the bacteria themselves. The level of fusion detected when fluid liposomes were mixed with Escherichia coli (66%) or P. aeruginosa (44%) seems to be correlated to their outer membrane phosphatidylethanolamine (PE) phospholipids composition (91% and 71%, respectively). Divalent cations increased the degree of fusion in the sequence Fe(2+) > Mg(2+) > Ca(2+) > Ba(2+) whereas temperatures lower than the phase transition temperature of DPPC/DMPG (9:1) vesicles decreased their fusion capacity. Acidic as well as basic pHs conferred higher degrees of fusion (54% and 45%, respectively) when compared to neutral pH (35%).
  
  
  CONCLUSIONS
  Based on the results of this study, a possible mechanism involving cationic bridging between bacterial negatively charged lipopolysaccharide and fluid liposomes DMPG phospholipids was outlined. Furthermore, the fluid liposomal-encapsulated tobramycin was prepared, and the in vitro bactericidal effects were also investigated.
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi.
authors: Zhao
authors: Z
authors: Wang
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an; School of Medicine, Xi'an Jiaotong University, Xi'an, People's Republic of China.
authors: Yufan
authors: Y
authors: Ma
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi.
authors: Hayssam
authors: H
authors: Khalil
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an.
authors: Rutao
authors: R
authors: Wang
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi.
authors: Tingli
authors: T
authors: Lu
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi.
authors: Wen
authors: W
authors: Zhao
authors: Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an.
authors: Yang
authors: Y
authors: Zhang
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi.
authors: Jamin
authors: J
authors: Chen
authors: Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi; Shaanxi Liposome Research Center, Xi'an, Shaanxi; Xi'an Libang Pharmaceuticals Co, Ltd, Xi'an.
authors: Tao
authors: T
authors: Chen
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology; D002118:Calcium / Q000737:chemistry; D002784:Cholesterol / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry / Q000187:drug effects; D008081:Liposomes / Q000737:chemistry*; D008561:Membrane Fusion / Q000187:drug effects; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry; D011550:Pseudomonas aeruginosa / Q000737:chemistry* / Q000187:drug effects; D013696:Temperature; D014031:Tobramycin / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D008081:Liposomes; D010714:Phosphatidylethanolamines; D010715:Phosphatidylglycerols; D010743:Phospholipids; D015060:1,2-Dipalmitoylphosphatidylcholine; C483858:phosphatidylethanolamine; D002784:Cholesterol; C002773:dimyristoylphosphatidylglycerol; D002118:Calcium; D014031:Tobramycin
keywords: fusion; lipid composition; lipid-mixing assay