The present study investigated the differences between lipopolysaccharide (LPS) and exopolysaccharide (EPS) in respect to immunological and physical-chemical characterization for possible uses as candidate vaccines against intra-peritoneal (I/P) challenge of virulent Aeromonas hydrophila in mouse model referring to Escherichia coli Dh5α as avirulent strain. There were only small differences among these antigen preparations with respect to their ability to elicit the titer of IgM, their activity in protection against lethal doses challenge, or their toxicity in mice through the follow up of liver enzymes, urea and weight changes. The differences which occurred between different antigens were in the degree of protection. The results indicated that capsular or EPS antigens (vaccines) confer the highest protective immunization. To study the immune response we estimated antibody titers and evaluated the protection by calculating the relative percent survival (RPS) after intra-peritoneal (I/P) injection and bath challenge of the pathogen. The physical-chemical characterization of used EPS and LPS fractions was done through the use of UV- spectra, IR, H-NMR and esstimation of total lipid.
Key words: Aeromonas hydrophila, Escherichia coli, exopolysaccharide, lipopolysaccharide
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