Isolation and characterization of immunogenic fractions from a Philippine strain Pasteurella multocida (Rosenbusch and Merchant, 1939) group A for the development of a potential subunit vaccine for animals

Fowl cholera caused by Pasteurella multocida group A can be prevented by an effective vaccine by the use of specific immunogenic fraction as the active component in a vaccination program. At present, fowl cholera vaccines are produced using the whole cell of the organism. Thus, the study was conducted in search of a cell fraction that can be used as an effective antigen for subunit vaccine. The lipopolysaccharide-protein complex (LPS), crude capsular antigen (CCA), ribosomal fraction (RS), and outer cell layer (OCL) were isolated from a Philippine duck strain of P. multocida Group A (PMA-Fs) as candidate immunogenic components for subunit vaccines. By the use of chicken peripheral blood to select the most immunogenic fraction as active component in the production of a subunit vaccine against fowl cholera, LPS and CCA were shown to be potential candidates. Antigenic characterization using plaque-forming cell assay, studies on the effect on the expression of putative gene marker molecules on the cell surfaces and phagocytic responses on chicken leuokocytes, all showed the potential antigenicity of either LPS or CCA as subunit vaccine component. When each of the fractions and the whole cells were used as key active components in the formulation of vaccines in active mouse protection test and challenged with lethal dose of the live P. multocida Group A, LPS and CCA subunit vaccines' potency were comparable with the whole cell control. RS and OCL fractions did not pass the AMPT, LPS- and CCA-stimulated groups of chicken also gave significant hemagglutinin titers against Brucella abortus- sheep red blood cells immunization and bovine serum albumin-induced delayed- typed hypersensitivity responses on chicken. These results indicated that LPS and CCA are potential protective active components for subunit vaccines against fowl cholera with indications that CCA has an advantage over LPS in all assay used. The use of these components has the advantage of producing more specific and potentially more effective vaccine against fowl cholera