<div><p>The Gram-negative saprophytic bacterium <i>Burkholderia pseudomallei</i> is the causative agent of melioidosis, a severe infectious disease of both humans and animals. Severity of the disease is thought to be dependent on both the health status of the host, including diabetes mellitus and kidney disease, and bacterial-derived factors. To identify the bacterial factors important during an acute infection, gene expression profiles in the spleen, lung, and liver of BALB/c (Th2 prototype) and C57BL/6 mice (Th1 prototype) were determined using DNA microarrays. This analysis identified BPSS1521 (<i>bprD</i>), a predicted transcriptional regulator located in the type III secretion system (T3SS-3) operon, to be up regulated, specifically in C57BL/6 mice. BALB/c mice infected with a <i>bprD</i> mutant showed a shorter time to death and increased inflammation, as determined by histopathological analysis and enumeration of bacteria in the spleen. Elevated numbers of multinucleated giant cells (MNGCs), which is the hallmark of melioidosis, were detected in both the wild-type and the <i>bprD</i> mutants; a similar elevation occurs in melioidosis patients. One striking observation was the increased expression of BPSS1520 (<i>bprC</i>), located downstream of <i>bprD</i>, in the <i>bprD</i> mutant. BprC is a regulator of T6SS-1 that is required for the virulence of <i>B. pseudomallei</i> in murine infection models. Deletion of <i>bprD</i> led to the overexpression of <i>bprC</i> and a decreased time to death. <i>bprD</i> expression was elevated in C57BL/6 —as compared to BALB/c—mice, suggesting a role for BprD in the natural resistance of C57BL/6 mice to <i>B. pseudomallei</i>. Ultimately, this analysis using mice with different immune backgrounds may enhance our understanding of the outcomes of infection in a variety of models.</p></div
