Characterization of BPSS1521 (bprD), a Regulator of Burkholderia pseudomallei Virulence Gene Expression in the Mouse Model

Abstract

The Gram-negative saprophytic bacterium Burkholderia pseudomallei 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 (bprD), 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 bprD 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 bprD mutants; a similar elevation occurs in melioidosis patients. One striking observation was the increased expression of BPSS1520 (bprC), located downstream of bprD, in the bprD mutant. BprC is a regulator of T6SS-1 that is required for the virulence of B. pseudomallei in murine infection models. Deletion of bprD led to the overexpression of bprC and a decreased time to death. bprD 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 B. pseudomallei. Ultimately, this analysis using mice with different immune backgrounds may enhance our understanding of the outcomes of infection in a variety of models.

Quantitative Proteomic Analysis of Burkholderia pseudomallei Bsa Type III Secretion System Effectors Using Hypersecreting Mutants

“…In a previous study, when bprD was deleted along with bprB and bprC , there was no change in levels of transcription of other Bsa T3SS genes leaving the role of BprD as a regulator in doubt ( 48 ). More recently, a bprD mutant of B. pseudomallei K96243 was shown to have increased expression of bprC ( 80 ), a downstream gene in the same operon shown to be involved in regulation of the virulence-associated T6SS ( 81 ). The bprD mutant also showed decreased time to death in intraperitoneally inoculated BALB/c mice demonstrating its importance in vivo and indicating its possible role as a negative regulator of virulence ( 80 ).…”

“…More recently, a bprD mutant of B. pseudomallei K96243 was shown to have increased expression of bprC ( 80 ), a downstream gene in the same operon shown to be involved in regulation of the virulence-associated T6SS ( 81 ). The bprD mutant also showed decreased time to death in intraperitoneally inoculated BALB/c mice demonstrating its importance in vivo and indicating its possible role as a negative regulator of virulence ( 80 ). It is not without precedent that a regulator of the T3SS is also a substrate for secretion ( e.g.…”

Characterization of pathogenesis of and immune response to Burkholderia pseudomallei K96243 using both inhalational and intraperitoneal infection models in BALB/c and C57BL/6 mice

“…MNGCs, referred to as a “hallmark” of B . pseudomallei infection [ 55 ], have been reported in other studies of chronic melioidosis in mice [ 33 , 55 ], Madagascar hissing cockroaches [ 56 ], and in human autopsies [ 57 ]. Surprisingly, there are few descriptions of MNGCs in mice infected with B .…”

“…Surprisingly, there are few descriptions of MNGCs in mice infected with B . pseudomallei [ 33 , 55 ].…”

The Impact of Age and Sex on Mouse Models of Melioidosis

“…While this sex bias observed in melioidosis may be primarily associated with health and/or occupational risk factors (e.g., alcoholism or occupational exposure through rice cultivation), it is important to examine both sexes of mice in order to get the most complete dataset possible [40]. There have been several reports using male mice as melioidosis models [41][42][43][44][45][46][47][48][49][50][51], but only a few have actually either compared males and females or characterized the disease pathology within male mice [41,[52][53][54]. Emery et al reported evidence demonstrating that female mice in their experiments tended to be more resistant to infection caused by intranasal instillation of B. pseudomallei [53].…”