Fig 4. SPI-1 virulence gene expression change in WT Salmonella upon treatment with 1 mM indole.

SPI-1 reporter strains for hilA, prgH, invF and sipC 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 mean fold decrease in expression (n = 3) with indole-treatment relative to the solvent-treated control at a significance level of p < 0.05 using the Student’s t-test. Error bars represent SD.