M.W. SHAFAA *, S.A. DAYEM**, W.M. ELSHEMEY***, H.M. OSMAN**
* Physics Department, Faculty of Science, Helwan University, Cairo, Egypt
** Research Institute of Ophthalmology, Giza, Egypt
*** Biophysics Department, Faculty of Science, Cairo University, Giza, Egypt
Abstract. Liposomes encapsulating antibiotics have always shown improved therapeutic index and reduced toxicity. Among the factors which affect the efficacy of liposomes loaded with antibacterial agents are the surface charge on liposomes and the interaction of the antibiotic with phospholipid vesicles. In this work, the incorporation of cephalexin (antibiotic) with neutral, negative and positive liposomes was studied using phase transition measurements. The main transition temperature of neutral liposomes was shifted to 42.5 ºC when liposomes were loaded with cephalexin while the main transition temperature of empty liposomes was found to occur at 40.5 ºC. Negative liposomes encapsulating cephalexin showed a pre-transition at 32.5 ºC and a main transition at 42.5 ºC. Positive liposomes loaded with cephalexin showed a phase transition temperature, equal to 38 ºC. The characteristics of growth of Staphylococcus aureus were also studied after treatment with the given liposome formulations. These characteristics of bacterial growth were found to be highly correlated to the physical properties of the applied liposome complexes. The in vitro antibacterial effect of negative liposomes encapsulating cephalexin was found to be superior compared to neutral and positive liposome formulations.
Key words: liposomes, antibiotics, cephalexin, Staphylococcus, aureus, phase transition.
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