Deletion of Polyamine Transport Protein PotD Exacerbates Virulence in Glaesserella (Haemophilus) parasuis in the Form of Non-biofilm-generated Bacteria in a Murine Acute Infection Model

Polyamines are small, polycationic molecules with a hydrocarbon backbone and multiple amino groups required for optimal cell growth. The <i>potD</i> gene, belonging to the ABC (ATP-binding cassette) transport system <i>potABCD</i>, encodes the bacterial substrate-binding subunit of the polyamine transport system, playing a pivotal role in bacterial metabolism and growth. The swine pathogen <i>Glaesserella parasuis</i> possesses an intact <i>pot</i> operon, and the studies presented here mainly examined the involvement of PotD in <i>Glaesserella</i> pathogenesis. A <i>potD</i>-deficient mutant was constructed using a virulent <i>G. parasuis</i> strain SC1401 by natural transformation; immuno-electron microscopy was used to identify the subcellular location of native PotD protein; an electron microscope was adopted to inspect biofilm and bacterial morphology; immunofluorescence technique was employed to study cellular adhesion, the levels of inflammation and apoptosis. The TSA++-pre-cultured mutant strain showed a significantly reduced adhesion capacity to PK-15 and MLE-12 cells. Likewise, we also found attenuation in virulence using murine models focusing on the clinical sign, H&amp;E, and IFA for inflammation and apoptosis. However, when the mutant was grown in TSB++, virulence recovered to normal levels, along with a high level of radical oxygen species formation in the host. The expression of PotD could actively stimulate the production of ROS in Raw 264.7. Our data suggested that PotD from <i>G. parasuis</i> has a high binding potential to polyamine, and is essential for the full bacterial virulence within mouse models. However, the virulence of the <i>potD</i> mutant is highly dependent on its TSA++ culture conditions rather than on biofilm-formation.