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Potential use of a liposome-encapsulated mixture of lipopolysaccharide core types (R1, R2, R3 and R4) of Escherichia coli in controlling colisepticaemia in chickens

¹ University of Peradeniya, Sri Lanka;

² Veterinary Research Institute, Gannoruwa, Sri Lanka;

³ University of Edinburgh

⁴ E-mail: i.r.poxton{at}ed.ac.uk

Received July 23, 2009
Accepted September 25, 2009

Infections caused by Escherichia coli make an economically significant impact in the poultry industry and a non-serotype-specific vaccine appears to be the most logical method of controlling it. The core oligosaccharide-lipid A region of bacterial lipopolysaccharide (LPS) is well conserved and highly immunogenic but toxic. This study determined the possible use of a liposome encapsulated mixture of rough LPSs of core types R1, R2, R3 and R4 in controlling infections caused by E. coli in chickens. The liposome which encapsulated LPS consisted of egg phosphatidylcholine, bovine brain phosphatidylserine and cholesterol. As determined by Limulus amoebocyte lysate assay, the endotoxicity of liposome incorporated LPS was at least 700 times lower than free LPS. Induction of nitric oxide production and expression of inflammatory genes by free LPS and liposome-incorporated LPS, when tested on chicken macrophage cell line (HD11), showed that liposome incorporated LPS produced a significantly lower amount of nitric oxide (>5 µM) than free LPS (22 µM). Transcription of the genes for interleukin-1 beta (IL-1β) and inducible nitric oxide synthase (iNOS) were lower in cells treated with liposome incorporated LPS than in cells treated with free LPS. Chickens when immunized with 0.2µg, 1 µg and 5 µg of liposome encapsulated mixture of LPS core types showed that the antibody response increased with increasing dose and the birds which received 5µg of liposome encapsulated LPS had significantly higher (p<0.001) anti-LPS core antibody titres than the chickens in all other groups and this also protected the birds against lethal challenge with E. coli O78.