|M.Sc Student||Estrin Elena|
|Subject||Using Liposomes to Enhance the Antibacterial Activity of|
|Department||Department of Biotechnology||Supervisor||Professor Timor Baasov|
|Full Thesis text|
The emergence of antibiotic resistance in gram-negative bacteria has sustained a continuing search for new agents with antibacterial activity against this important class of bacterial pathogen. The lipopolysaccharide is a unique component of the outer membrane of gram negative bacteria and is required for their growth and virulence. Due to its importance, attempts have been made to discover antibacterial agents that inhibit enzymes involved in the biosynthesis of LPS. The unusual 8-carbon sugar 3-deoxy-D-manno-2-octulosonic acid (KDO) is a site-specific constituent of the LPS. Mutants defective in KDO biosynthesis are not viable, and since the biosynthesis and incorporation of KDO has been well studied, much effort has been devoted toward design of synthetic inhibitors against the biosynthesis of KDO. The first committed step in the biosynthesis of KDO is catalyzed by the enzyme 3-deoxy-D-manno-octulosonate 8-phosphate synthase. Inhibitor 2, is a potent inhibitor of the KDO8PS (Ki = 0.4 μM), which was developed in our lab, following systematic mechanistic and structure-activity studies. Antibacterial tests against a series of different Gram-negative organisms revealed that inhibitor 2 lacks antibacterial activity, probably due to its reduced ability to penetrate the bacterial cell membrane. In the light of recent achievements that demonstrated the ability of liposomes to help antibiotics to penetrate the microbial cell membrane, we chose this methodology for solving the impermeability problem of the inhibitor 2 in Gram-negative bacterial cell. We have encapsulated the inhibitor 2 into a fluid liposomal formulation, which consisted of DPPC and DMPG phospholipids in a molar ratio of 10:1. The results showed for the first time antibacterial activity of the liposome-encapsulated inhibitor 2 against several E.coli strains in vitro, while the free inhibitor 2 did not show any antibacterial activity. Our data suggest that liposome-entrapped inhibitor 2 can provide new formulation of antibacterial drug selectively directed against Gram-negative bacteria.