Invasion of endothelial cells by systemic and nasal strains of Haemophilus parasuis

Haemophilus parasuis is a respiratory commensal in healthy piglets, but can also produce invasive disease and meningitis, which requires the ability to cross the blood–brain barrier. This study determined the capacity of well-characterised virulent and non-virulent strains of H. parasuis, as well as other field strains, to adhere to and invade PBMEC/C1-2 endothelial cells. Virulent strains were derived from systemic lesions, conformed to the systemic clade on multilocus sequence typing (MLST) and were phagocytosis- and serum-resistant. Non-virulent strains were derived from the nostrils of healthy piglets, belonged to the nasal clade on MLST and were phagocytosis- and serum-sensitive. Virulent strains mostly were more invasive than non-virulent strains, although one virulent strain was unable to invade. Invasion of endothelial cells is a virulence mechanism of H. parasuis that may be related to the ability of some strains to cause meningitis.