Enhancement of the antibacterial activity of ampicillin by liposome encapsulation

Abstract

This study showed that encapsulation of ampicillin (Amp) in liposomes prepared with synthetic lecithins enhanced its antibiotic activity against both Amp-sensitive and Amp-resistant Escherichia coli. This was demonstrated by growth inhibition of E. coli in the presence of the liposomal preparations containing Amp. Growth inhibition was also seen in the presence of exogenous β-lactamase. Adsorption of Amp onto the surface of the liposomes did not result in enhanced activity of the drug against E. coli. The encapsulation efficiency of Amp in liposomes prepared by the Bangham method (BM) was greatly affected by the phospholipids used. The efficiency increased with a rise in the phase transition temperature (T_c) of the phospholipid, the maximum encapsulation of Amp being obtained with distearoylphosphatidylcholine (DSPC). The entrapment efficiency of Amp with the reverse phase evaporation method (REV) was largely superior to that with the BM method. Kinetic studies using DSPC liposomes prepared by the REV and BM protocols demonstrated that Amp-loaded liposomes contained 60 and 72% of drug, respectively, after 24 h at 37°C.

Key Words :

• Ampicillin
• Antibiotic Resistance
• Escherichia coli
• β-lactamase
• Liposomes
• Phospholipids