An isogenic Actinobacillus pleuropneumoniae AasP mutant exhibits altered biofilm formation but retains virulence

AasP, an autotransporter serine protease of Actinobacillus pleuropneumoniae, has been shown to be expressed in necrotic porcine lung tissue. Based on the hypothesis that AasP might play an important role in A. pleuropneumoniae adhesion and virulence by processing other surface-associated proteins, the predicted catalytic site of AasP was deleted and the isogenic mutant, AP76ΔaasP, was compared to the wild-type strain in a biofilm assay as well as an aerosol infection model. AP76ΔaasP showed increased adherence compared to the wild-type strain under standard culturing conditions as well as under NAD restriction. No significant differences between AP76 wild-type and AP76ΔaasP were observed upon experimental infection of pigs, indicating that AasP does not play a crucial role in A. pleuropneumoniae virulence.