INFECTION OF CULTURED RAT ENTEROCYTES BY ILEAL SYMBIONT INTRACELLULARIS DEPENDS ON HOST-CELL FUNCTION AND ACTIN POLYMERIZATION

The mechanisms of entry of Ileal symbiont intracellularis into IEC-18 rat enterocyte cells and subsequent bacterial proliferation were exami ned in centrifuge-assisted and static infections. Live, oxygen or neom ycin damaged, and formalin killed bacteria, each rapidly entered viabl e cells. Live or damaged bacteria did not enter cells nor proliferate within cells after static infection of cells cooled to 5 degrees C. In fection of cells was greatly reduced at 20 degrees or 32 degrees compa red to infection at 37 degrees C. Centrifuge-assisted infection was al so reduced by chilling the cells. Cytochalasin D but not B inhibited t he entry process indicating an actin-dependent infection, although oth er pathways may also be involved in centrifuge-assisted infections. Dr ugs capable of modifying cell membrane charge, heparin receptors or tr ypsin-labile proteins were all inactive in preventing or enhancing inf ection. We therefore conclude that infection of enterocytes by IS intr acellularis is dependent on host cell activity and actin polymerizatio n, but is independent of bacterial viability.