It is noteworthy that transcription of the invasion-associated Salmonella pathogenicity island-1 genes homologous to the bsa locus is activated by the addition of NaCl [26]. Gaining an understanding of the ability of B. pseudomallei to survive in the presence of high salt concentrations is therefore learn more significant, as this may provide insights into its pathogenicity and persistence in endemic areas. Here we used a genome-wide oligonucleotide microarray to quantify the transcription of B. pseudomallei genes

in response to salt stress. Differential regulation of a subset of genes was confirmed by RT-PCR and by analysis of production of the encoded proteins. Our data reveal that exogenous NaCl induces the virulence-associated Bsa T3SS and the consequences this website of such for invasion of A549 cells were investigated. Results B. pseudomallei growth was inhibited in high salt To better understand

the physiology of B. pseudomallei in response to elevated salt, we titrated the effect of salt on B. pseudomallei growth starting from salt-free Luria Bertani (LB) medium and standard LB medium containing 170 mM plus various concentrations of NaCl (170+150, 170+300 and 170+450 mM), and found that conditions with 470 and 620 mM NaCl had severe impairment on B. pseudomallei growth (data not shown). For lower NaCl concentrations, the growth kinetics of B. pseudomallei K96243 cultured in standard LB medium containing 170 or 320 mM NaCl was similar until 6 hrs; the growth rate thereafter was impaired when cultured in LB broth containing 320 mM NaCl (Figure 1). The doubling time in NaCl-supplemented LB broth was calculated to be 53 ± 4.3 min compared to 38 ± 3.0 min in standard LB broth (t-test; P value

all = 0.027). In addition, we found that growth of B. pseudomallei in salt-free medium was faster than in standard LB medium supplemented with 170 and 320 mM NaCl (Figure 1). This data indicated that increased NaCl reduced the logarithmic growth rate of B. pseudomallei. Figure 1 Growth kinetics of B. pseudomallei. B. pseudomallei K96243 growth in LB broth containing 0, 170 or 320 mM NaCl was determined by colony plate counting. The data points and error bars represent mean colony forming unit (CFU) and standard deviation from triplicate experiments. Differential transcriptome of B. pseudomallei during growth in high salt Our studies indicated that growth of B. pseudomallei was severely impaired during culture at NaCl concentrations of 470 and 620 mM (data not shown). This suggested that these concentrations may be too high to detect salt-specific transcriptional changes. A previous study carried out in our laboratory demonstrated a U0126 purchase significantly altered secretome when the organism was grown in 320 mM NaCl compared to standard LB medium (170 mM NaCl) [16].