To confirm that some siRNA pools specifically affected cell-to-cell spread, we examined the effect of 85 siRNAs from the original screen on infection of endothelial cells with an ActA-deficient strain (JAT1045) that is incapable of cell-to-cell spread; we included siRNAs that exhibited increased bacterial density per infected cell (siCAPZA2, siACTR2) or decreased focus size (siRACGAP1, siSTX16, siMAP1LC3A) in the original screen, expecting that these siRNA pools should not have a significant phenotype in this assay. This evidence concerns the gene ACTA1 and infection.