Construction and immunization with double mutant Δ Δ forms of serotypes 1 and 5.

(APP) causes a form of porcine pleuropneumonia that leads to significant economic losses in the swine industry worldwide. The gene is responsible for the secretion of the ApxI and ApxII toxins and the gene is responsible for the adaptation of bacteria to cold temperature and a virulence factor. The and genes were deleted successfully from APP serotype 1 and 5 by transconjugation and sucrose counter-selection. The APP1ΔΔ and APP5ΔΔ mutants lost hemolytic activity and could not secrete ApxI and ApxII toxins outside the bacteria because both mutants lost the ApxI- and ApxII-secreting proteins by deletion of the gene. Besides, the growth of these mutants was defective at low temperatures resulting from the deletion of . The APP1ΔΔ and APP5ΔΔ mutants were significantly attenuated compared with wild-type ones. However, mice vaccinated intraperitoneally with APP5ΔΔ did not provide any protection when challenged with a 10-times 50% lethal dose of virulent homologous (APP5) and heterologous (APP1) bacterial strains, while mice vaccinated with APP1ΔΔ offered 75% protection against a homologous challenge. The ΔΔ mutants were significantly attenuated and gave different protection rate against homologous virulent wild-type APP challenging.