Liposomes loaded with rifampicin and tobramycin for anti-staphylococcus aureus action

Reducing patient recovery time and potential post surgical complications of warfighters after traumatic injury is of importance for the military. However, a current medical challenge in treating warfighters with traumatic injuries is bacterial infection due to multi-drug resistant bacteria. These infections can delay wound healing and increase the rate of mortality in severe cases of infections. We are developing a nanosystem that preserves functionality and controls delivery of antibiotics for an extended period of time. This system is expected to exert antibacterial activity for a broad spectrum of bacterial species. In this study, we investigated the particle size, entrapment efficiency, and antibacterial activities of two antibiotics, rifampicin and tobramycin, [active against Staphylococcus aureus (S.a, ATCC 12600) and Methicillin-resistant strain of S.a (MRSA, BAA-1720)] in liposomes synthesized by a modified dehydration-rehydration liposome method. Encapsulation efficiency of liposomes decreased with decrease in drug concentration, and was also affected by the type of drug encapsulated. For rifampicin, initial drug loadings of 20 mg, 10 mg, 5 mg and 2.5 mg resulted in entrapment efficiencies of 64.8 ± 17.3%, 49.6 ± 1.9, 39.2 ± 9.7%, and 36.9 ± 5.9%, respectively, and for tobramycin entrapment efficiencies were 26.7 ± 4.7%, 24.3 ± 5.3% and 22.5 ± 3.5% and 19.4 ± 3.7%, respectively. The average particle sizes of liposomes in the mixture was approximately 200-300 nm and 300-500 nm for tobramycin and rifampicin, respectively, and they also varied depending on the amount of drug that was used for liposome synthesis. In vitro antibiotic release studies were performed for 7-9 days in phosphate-buffered saline (PBS) at 37°C. The results demonstrated that liposomes released sufficient amount of antibiotics, and antibacterial activities were preserved over this period against S.a. Currently, we are investigating a variety of ways to incorporate these liposome systems into various antimicrobial agent delivery systems.