Activation of caspase-3 was noted in epithelial cells within the loops after 30 min of infection, but in the ΔSipA/SipA-phiLOV-infected loops this activation was accompanied by an intense green fluorescent signal within caspase-3-positive cells that was absent in SL1344 loops (Fig. 6A). This evidence concerns the gene CASP3 and infection.