COMPLEMENTATION OF A DNAK-DEFICIENT ESCHERICHIA-COLI STRAIN WITH THE DNAK DNAJ OPERON OF BRUCELLA-OVIS REDUCES THE RATE OF INITIAL INTRACELLULAR KILLING WITHIN THE MONOCYTIC CELL-LINE U937/

Facultatively intracellular bacteria express heat shock proteins after phagocytosis by macrophages. Using non-pathogenic Escherichia coli st rains and the human monocytic cell line U937, we showed that deletion of the dnaK gene significantly increased the rate of initial intracell ular killing of bacteria. Trans-complementation of the deletion mutant with the dnaK/dnaJ operon of Brucella ovis restored the pattern of in tracellular elimination of the control strain expressing dnaK. These d ifferences were not observed using antibody-opsonized bacteria and act ivated cells. In vitro, strains expressing dnaK resisted hydrogen pero xide better than the deletion mutant; in contrast, the mutant compleme nted by dnaK/dnaJ of B. ovis tolerated low pH and low H2O2 better than the wild-type strain and the deletion mutant. Our results suggested t he participation of DnaK in protection of intracellular bacteria again st antimicrobial macrophage factors.