realized in has disposition at some time agent_in_compromised_process Brucella intracellular replication in macrophage artificially mutated Brucella macrophage - Brucella interaction attenuated disposition B. suis dnaK mutant MUTATION: The heat shock protein DnaK is essential for intramacrophagic replication of Brucella suis. The replacement of the stress-inducible, native dnaK promoter of B suis by the promoter of the constitutively expressed bla gene resulted in temperature-independent synthesis of DnaK. In contrast to a dnaK null mutant, this strain grew at 37 degrees C, with a thermal cutoff at 39 degrees C However, the constitutive dnaK mutant, which showed high sensitivity to H(2)O(2)-mediated stress , failed to multiply in murine macrophage-like cells and was rapidly eliminated in a mouse model of infection, adding strong arguments that stress-mediated and heat shock promoter-dependent induction of dnaK is a crucial event in the intracellular replication of B suis [Ref6500:Köhler et al., 2002]. Mutation studies indicated that DnaK, but not DnaJ, was required for growth at 37 degrees C in vitro. Viability of the dnaK null mutant was also greatly affected at low pH. In infection experiments performed with both mutants at the reduced temperature of 30 degrees C, the dnaK mutant of B suis survived but failed to multiply within U937 cells, whereas the wild-type strain and the dnaJ mutant multiplied normally. Complementation of the dnaK mutant with the cloned dnaK gene restored growth at 37 degrees C, increased resistance to acid pH, and increased intracellular multiplication [Ref6500:Köhler et al., 2002]. See PMID:11854256