Comparison of BABAR -normalised microarray data with RT-PCR analyses. The relative expression levels for 13 Salmonella genes from inside epithelial cells (2 h p.i. or 6 h p.i. vs. mid-exponential LB control cultures) as determined by microarray analysis (BABAR normalisation) and RT-PCR are shown (Pearson correlation coefficient = 0.83, p < 0.001; r2 = 0.69 via linear regression). For the RT-PCR analyses, RNA was independently extracted from LB cultures of Salmonella or from Salmonella cells internalised in epithelial cells, and used in RT-PCR amplification of the genes of interest.