FIG. 5.
Intramacrophage growth and virulence of the lpeA mutant of L. monocytogenes. □, wild-type EGD-e; ▵, lpeA mutant. (A) Growth of L. monocytogenes in bone marrow-derived macrophages from C57/BL6 mice. The cells were exposed for 15 min (time zero) to bacteria (1 bacterium per cell), and bacterial survival was monitored for 6 h after the infection. Entry was very efficient in both strains, and mutant bacteria repeatedly grew faster in macrophages (*, P < 0.001). (B and C) Growth of L. monocytogenes in the spleen (B) and the liver (C) of Swiss mice inoculated i.v. with 105 bacteria. Mutant bacteria grew faster in organs (*, P < 0.007) than did wild-type bacteria, and they induced an early mortality in mice by day 3.