In vitro treatment of lipopolysaccharide increases invasion of Pasteurella multocida serotype B:2 into bovine aortic endothelial cells

Seng Kar Yap, Zunita Zakaria, Siti Sarah Othman, Abdul Rahman Omar

Pasteurella multocida serotype B:2 causes haemorrhagic septicaemia (HS) in cattle and buffaloes. The invasion mechanism of the bacterium to invade the bloodstream is unclear. This study aims to characterize the effects of immunomodulatory molecules, namely dexamethasone and lipopolysaccharide treatments, on the invasion efficiency of P. multocida serotype B:2 towards bovine aortic endothelial cells (BAECs) and the involvement of actin microfilament in the invasion mechanism. The results imply that treatment of BAECs with lipopolysaccharide at 100 ng/mL for 24 h significantly increases the intracellular bacteria number per cell (P<0.01) compared with untreated and dexamethasone-treated cells. The lipopolysaccharide-treated cells show a significant decrease of F-actin and an increase of G-actin expressions (P<0.001), indicating actin depolymerization of BAECs. However, no significant differences were detected in the invasion efficiency and actin filaments reorganization between the dexamethasone-treated cells and the untreated cells. Transmission electron microscopy (TEM) showed P. multocida B:2 resided in a vacuolar compartment of dexamethasone-treated and untreated cells, whereas the bacteria resided in cellular membrane of lipopolysaccharide-treated cells. The findings suggest that lipopolysaccharide destabilizes the actin filaments of BAECs which could facilitate the invasion of P. multocida B:2 into BAECs.