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Actinobacillus pleuropneumoniae (APP) causes porcine pleuropneumonia, a disease responsible for substantial losses in the worldwide pig industry. In this study, outbred Kunming (KM) and Institute of Cancer Research (ICR) mice were evaluated as alternative mice models for APP research. After intranasal infection of serotype 5 reference strain L20, there was less lung damage and a lower clinical sign score in ICR compared to KM mice. However, ICR mice showed more obvious changes in body weight loss, the amount of immune cells (such as neutrophils and lymphocytes) and cytokines (such as IL-6, IL-1β and TNF-α) in blood and bronchoalveolar lavage fluid (BALF). The immunological changes observed in ICR mice closely mimicked those found in piglets infected with L20. While both ICR and KM mice are susceptible to APP and induce pathological lesions, we suggest that ICR and KM mice are more suitable for immunological and pathogenesis studies, respectively. The research lays the theoretical basis for determine that mice could replace pigs as the APP infection model and it is of significance for the study of APP infection in the laboratory., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Pili have been demonstrated to contribute to the pathogenicity of many bacterial pathogens. Flp pilus encoded by the tad locus belongs to the type IVb pilus. Our previous study has revealed that the intact tad locus is essential for Flp pilus formation in Actinobacillus pleuropneumoniae, a very important porcine respiratory pathogen. To further investigate the functions of Flp pilus in A. pleuropneumoniae pathogenesis, the flp1 and tadD single deletion mutants were constructed by homologous recombination. Both of the mutant strains lost pilus on their cell surfaces. The abilities of biofilm formation, cell adhesion, resistance to phagocytosis, survival in swine whole blood, and in vivo colonization of the two mutants were significantly reduced compared with those of the parental strain. The corresponding complemented strains recovered the phenotypes. These results demonstrated that flp1 and tadD were essential for the biosynthesis of Flp pilus and that the pilus played important roles during infection of A. pleuropneumoniae., (Copyright © 2018 Elsevier Ltd. All rights reserved.)