Haemophilus parasuis is the agent responsible for causing Gla¨ sser’s disease, which is
characterized by fibrinous polyserositis, polyarthritis and meningitis in pigs. The purpose
of this study was to investigate the in vitro ability of two H. parasuis serovars of different
virulence (serovar 5, Nagasaki strain, highly virulent, belonging to serovar 5, and SW114
strain, nonvirulent, belonging to serovar 3) to adhere to and invade porcine kidney
epithelial cells (PK-15 line). Nagasaki strain was able to attach at high levels from 60 to
180 min of incubation irrespective of the concentrations compared (107–1010 CFU), and a
substantial increase of surface projections could be seen in PK-15 cells by scanning
electron microscopy. This virulent strain was also able to invade effectively these
epithelial cells, and the highest invasion capacity was reached at 180 min of infection. On
the contrary, nonvirulent SW114 strain hardly adhered to PK-15 cells, and it did not invade
these cells, thus suggesting that adherence and invasion of porcine kidney epithelial cells
could be a virulence mechanism involved in the lesions caused by H. parasuis Nagasaki
strain in this organ
