title: Characterization and immunogenicity of an apxIA mutant of Actinobacillus pleuropneumoniae.
abstract: Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a highly contagious and often fatal disease. A candidate live vaccine strain, potentially capable of cross-serovar protection, was constructed by deleting the section of the apxIA gene coding for the C-terminal segment of ApxI toxin of the A. pleuropneumoniae serovar 10 reference strain (D13039) and inserting a chloramphenicol resistance gene cassette. The mutant strain (termed D13039A(-)Chl(r)) produced an approximately 48kDa protein corresponding to the N-terminus of the ApxI toxin, and exhibited no haemolytic activity and lower virulence in mice compared with the parental strain. The mutant was evaluated in a vaccination-challenge trial in which pigs were given two intra-nasal doses of the mutant at 14 days intervals and then challenged 14 days after the last vaccination with either A. pleuropneumoniae serovar 1 (4074) or serovar 2 (S1536) or serovar 10 (D13039) reference strains. The haemolysin neutralisation titres of the pre-challenge sera were significantly higher in the vaccinated pigs than in the unvaccinated pigs. The mortalities, clinical signs and lung lesion scores in the vaccinated pigs were significantly lower than those in the unvaccinated pigs for the serovar 1 challenge. A significantly lower lung lesion score was also observed in the vaccinated pigs, compared with unvaccinated pigs, for serovar 2 challenge. Our work suggests that the mutant strain offers potential as a live attenuated pleuropneumonia vaccine that can provide cross-serovar protection.
authors.affiliation: Key Laboratory of Preventive Veterinary Medicine of Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Haidian District, Beijing, China.
authors.forename: Fuzhou
authors.initials: F
authors.lastname: Xu
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Chen
authors.forename: Aihua
authors.initials: A
authors.lastname: Shi
authors.forename: Bing
authors.initials: B
authors.lastname: Yang
authors.forename: Jinluo
authors.initials: J
authors.lastname: Wang
authors.forename: Yongqing
authors.initials: Y
authors.lastname: Li
authors.forename: Xin
authors.initials: X
authors.lastname: Guo
authors.forename: P J
authors.initials: PJ
authors.lastname: Blackall
authors.forename: Hanchun
authors.initials: H
authors.lastname: Yang
mesh_terms: D000189:Actinobacillus Infections / Q000382:microbiology / Q000401:mortality / Q000517:prevention & control / Q000662:veterinary*; D016977:Actinobacillus pleuropneumoniae / Q000235:genetics* / Q000276:immunology* / Q000472:pathogenicity; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D001428:Bacterial Vaccines; D001681:Biological Assay / Q000662:veterinary; D005260:Female; D006460:Hemolysin Proteins / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D009500:Neutralization Tests / Q000662:veterinary; D011001:Pleuropneumonia / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary*; D011897:Random Allocation; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology / Q000401:mortality / Q000517:prevention & control*; D014613:Vaccines, Attenuated
chemical_list: D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D006460:Hemolysin Proteins; D014613:Vaccines, Attenuated; C087744:ApxI toxin, Bacteria