FIG. 1.

In vivo survival and replication of L. monocytogenes in the livers of infected mice. Livers of mice infected with L. monocytogenes LO28 (A to D) and an isogenic clpP mutant (E to H) were examined by light microscopy of semithin sections stained with toluidine blue (left panel) and by electronic microscopy of ultrathin sections (right panel). After 1 h, wild-type bacteria (A and B) and mutant bacteria (E and F) were confined inside Küpffer cells of sinusoid capillaries and appeared intact. After 8 h, dense clusters of wild-type bacteria were visible throughout the parenchyma, with invasion of adjacent hepatocytes (C). Electron microscopy showed replicating bacteria in the cytoplasm of hepatocytes with actin polymerization (D). Conversely, clpP mutant bacteria were hardly visible after 8 h, suggesting that they had been cleared by resident phagocytes (G); ghosts of mutant bacteria were seen inside vacuoles of rare Küpffer cells (H).