Expression of ripA in the intracellular niche. Intracellular expression of LVS ripA'-lacZ2 and LVS iglA'-lacZ in J774A.1 mouse macrophage like cells infected at an MOI of 100. Inoculums were either prepared from mid exponential phase bacteria grown in BHI (a) or CDM (b) as indicated in the legend. Preparation in CDM resulted in an increased initial activity in the reporter strains. All assays were performed on four replicate wells and reported as mean relative activity ± standard deviation. Inoculums activity was calculated from four samples taken before application of the inoculums. Mean β-galactosidase activity is normalized by time of development and CFU per well minus the activity from the control samples. All differences in expression were significant (P < 0.05) with the exception of comparisons between ripA'-lacZ2 inoculums to 6 h, and iglA'-lacZ 1 h to 24 h. The mean CFU recovered at each time point assayed are displayed as log CFU (c). Error bars represent the standard deviation of four samples. Each strain invaded and replicated by 24 hours in J774A.1 mouse macrophage like cells.