Infection of cultured rat enterocytes by Ileal symbiont intracellularis depends on host cell function and actin polymerisation.

The mechanisms of entry of Ileal symbiont intracellularis into IEC-18 rat enterocyte cells and subsequent bacterial proliferation were examined in centrifuge-assisted and static infections. Live, oxygen or neomycin damaged, and formalin killed bacteria, each rapidly entered viable cells. Live or damaged bacteria did not enter cells nor proliferate within cells after static infection of cells cooled to 5 degrees C. Infection of cells was greatly reduced at 20 degrees or 32 degrees compared to infection at 37 degrees C. Centrifuge-assisted infection was also reduced by chilling the cells. Cytochalasin D but not B inhibited the entry process indicating an actin-dependent infection, although other pathways may also be involved in centrifuge-assisted infections. Drugs capable of modifying cell membrane charge, heparin receptors or trypsin-labile proteins were all inactive in preventing or enhancing infection. We therefore conclude that infection of enterocytes by IS intracellularis is dependent on host cell activity and actin polymerization, but is independent of bacterial viability.