The Adh adhesin domain is required for trimeric autotransporter Apa1-mediated Actinobacillus pleuropneumoniae adhesion, autoaggregation, biofilm formation and pathogenicity

Actinobacillus pleuropneumoniae is a causative agent of porcine pleuropneumonia, which is a highly contagious endemic disease of pigs. Adhesion is a critical first step in the infection process. Trimeric autotransporter adhesions (TAAs) have been identified as novel virulence factors; however, little is known on their roles in A. pleuropneumoniae pathogenicity. Here, our data show that YadA-like head region (Adh) of Apal was the optimal adhesion functional domain via segment expression and adhesion assays in vitro. Additionally, Adh induced partial protection against A. pleuropneumoniae 5b L20 and serotypes 1, 3, and 5a in mice. The deletion of Adh gene significantly decreased autoaggregation, biofilm formation and adherence to host cells in vitro. Furthermore, with delaying of clinical symptoms, reducing production of pro-inflammatory cytokines and lessening the lung injury after infection, Adh deletion strain (5b(bAdh) significantly reduced the pathogenicity to piglets. To elucidate the mechanism of lung injury, the differentially expressed genes in the lung tissues of piglets infected with the 5b L20 or 5bcbAdh strains were investigated using microarray analysis and validated by gRT-PCR. Compared with the 5b L20 infected piglets, 495 genes were differentially expressed in 5b4)Adh infected lung tissue (221 upregulated and 274 downregulated). Especially, the antigen processing and presentation gene 1F130 was increased following infection with the 5b4Adh strain. Thus, Adh may enhance pathogenicity by depressing host immune recognition. We conclude that the head domain of the A. pleuropneumoniae trimeric autotransporter Apal regulates autoagglutination, biofilm formation, adhesion to host cells and pathogenicity. (C) 2015 Elsevier B.V. All rights reserved.