Antimicrobial activity of liposome encapsulated cyclo(L-tyrosyl-L-prolyl)

Various studies have shown the potentially beneficial biological activities of cyclic dipeptides and in particular, cyclo(L-tyrosyl-L-prolyl) (cyclo(Tyr-Pro)) has shown fair antibacterial activity in vitro. This study aimed to determine if liposome encapsulation would have any significant effects on the antibacterial activity of this compound. The thin-film hydration method with extrusion was used to produce small unilamellar vesicles containing cyclo(Tyr-Pro) that were shown to have an average encapsulation of 9.4% with a mean particle size of 160.4 nm. Minimum inhibitory concentrations tested against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Bacillus subtillis were shown to be lower in liposome encapsulated cyclo(Tyr-Pro) than for the free form, while no antimicrobial activity was noted for either encapsulated nor non-encapsulated drug against the fungus Candida albicans or two methicillin-resistant strains of Staphylococcus aureus (MRSA). A positive control of liposome encapsulated amoxicillin was shown to be extremely active against both MRSA strains. The results confirm that liposome encapsulation has the potential to enhance activity as well as to overcome bacterial resistance towards current antibacterial agents.