Characterisation of gene expression and virulence factors in Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is a Gram-negative bacterium causing the highly infectious disease porcine pleuropneumonia and is responsible for global financial losses to the swine industry every year. Though the virulence of A. pleuropneumoniae is complex and multifactorial, Apx toxins (ApxI-III) are the major contributing factors that causes lung lesions in pigs. Although vaccines are available to prevent A. pleuropneumoniae infections, they do not give complete protection and typically give protection against the serovars used to prepare the vaccine. Thus, a thorough understanding of gene expression and virulence factors is required to develop broadly protective pleuropneumonia vaccines. This thesis first investigated a novel pathway to prevent and treat pleuropneumonia infection by blocking the interaction between Apx toxins and the host cells. To determine the specific ligands bound by each Apx toxin, glycan array analysis using purified Apx toxins (ApxI-III, both the active and inactive forms e.g. ApxCA and ApxA) was carried out. Expressing both with and without ApxC allowed an assessment of whether this activation is required for interaction with the host glycan receptor. Significant work was needed to optimise overexpression and purification of Apx toxins. Glycan array analysis demonstrated that both ApxI and ApxII toxins bound to very similar glycan structures, such as gangliosides and Lewis antigens. Binding of Apx toxins occurred irrespective of activation by the cognate acyltransferase, ApxC. [...]
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Institute for Glycomics
Science, Environment, Engineering and Technology
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