To investigate the latter possibility, time course studies were undertaken which revealed similar numbers of intracellular bacteria for both Salmonella strains following a short (30 min; p = 0.6) infection period with significantly fewer intracellular SPI-1 mutant bacteria at later—180 (p < 0.02) or 300 (p < 0.002) minute – post-infection time points (Fig. 4e). Here, SPI1 is linked to infection.