Role of <i>phoPQ</i> in indole mediated down-regulation of virulence.

<p>(A) SPI-1 virulence gene expression using ß-gal assay. The Δ<i>phoPQ</i> mutation was generated in the four SPI-1 reporter strains for <i>hilA</i>, <i>prgH</i>, <i>invF</i> and <i>sipC</i>. The WT and the Δ<i>phoPQ</i> reporter strains were treated overnight with and without 1 mM indole and the ß-gal activity was measured in exponential phase cultures after dilution. Data shown are the fold decrease in expression with indole-treatment relative to the solvent-treated control. * denotes statistical significance relative to the WT strain at <i>p</i> < 0.05 using the Student’s <i>t</i>-test. (B) Invasion in HeLa epithelial cell line with <i>Salmonella</i> WT and Δ<i>phoPQ</i> strain treated with or without 1mM indole. A MOI of 100:1 was used and the data shown is the indole-treated <i>Salmonella</i> invasion normalized to the control of the respective strain. * denotes statistical significance with respect to the solvent control at <i>p</i> < 0.05 using the Student’s <i>t</i>-test. Column bars depict mean (n = 3) and error bars represent standard deviation (SD).