Immunogenic Characterization Of The N-terminal Polypeptide Of ApxIA Of Actinobacillus Pleuropneumoniae Serotype 1 And Construction Of A Recombinant Strain Of Serotype 7 Expressing The Polypeptide

Porcine contagious pleuropneumonia (PCP), caused by Actinobacillus pleuropneumoniae (APP), is porcine respiratory infectious disease leading severe economic losses worldwide in the swine industry.Immunization is the main method to prevent and control this disease. The available commercial vaccines are still primarity killed whole cell bacterins and subunit vaccines, which generally reduce mortality from APP infection but frequently fail to block the infection, resulting in decrease in growth rate and feed efficency of pigs.In contrast, natural and experimental infection can induce protection against any heterologous serotypes. Thus, live attenuated vaccines might be a viable approach to solve this problem. The previously described methods for the construction of mutant strains of A. pleuropneuminiae have some disadvantage. For example, mutagenesis using chemical or transposon mediated approaches presented a random approach and allowed for the selection of mutants with a distinct phenotype only; mutations not resulting in a distinct phenotype could not be constructed by these means. All these mutants, which is achieved by traditional mutagenesis approaches allowing targeted mutation by homologous recombination, however, carry a permanent antibiotic resistance marker and, therefore, are not suitable as vaccine strains. Bei etal deleted apxIIC gene from the strain HB of serotype 7 by homologous recombination using a sucrose counter selectable marker then get a antibiotics resistance markerless attenuated mutant apxIIC/GFP+. The resulted mutant HBC-/GFP+ without antibiotic resistance marker expressed a form of non-toxic ApxIIA, the structural protein of ApxII whose toxicity must be activated by ApxIIC encoded by apxIIC gene. This live attenuated strain could provide 100% and 75% protection against the homologous serotype 7 and heterologous serotype 1 respectively when inoculated piglets intranasally. The complete coding sequence of apxIA gene is 3146 bps, which is difficult to be introduced into the chromosome of APP by traditional recombination. We characterized the the immunogenecity of ApxIA and its protective epitopes, and tried to get the genetic engineering mutant strain apxIIC^?/apxIA5⁺, following researches were explored.1. Immunogenicity of the N-terminal Polypeptide of RTX Toxin I of Actinobacillus PleuropneumoniaeApxI is one of the most important virulence factors of Actinobacillus pleuropneumoniae (APP). To study the immunogenicity of the ApxI, the complete coding sequence (3146bp) and its 5'-terminal 1140 bp fragment of the apxI A gene were...