Requirement of selected virulence genes for intracellular growth in macrophages. (A) Diagrams visualizing the necessity of LIPI-1 genes during growth under standard growth conditions (BHI broth; blue) and during intracellular growth in J774 mouse macrophages (intracellular; red). Tn insertions are mapped on the chromosomal region carrying the LIPI-1 genes (prfA-lmo0206). Tn insertions are not found in genes that are required for growth under a certain condition. The prs gene preceding LIPI-1 is required for growth even under normal growth conditions. (B) Intracellular multiplication of L. monocytogenes strains EGD-e (wt), LMS250 (Δhly), LMS251 (ΔactA), and BUG2214 (ΔprfA) inside J774 mouse macrophages over a time course of 6 h. Strain LMS2 (ΔdivIVA) was included for comparison. The experiment was performed in triplicate. Average values and standard deviations are shown. (C) Intracellular replication of L. monocytogenes strains EGD-e (wt), LMS250 (Δhly), LMS2 (ΔdivIVA), LMS81 (ΔsecA2), and LMJR87 (ΔcozEb) mutants in J774 mouse macrophages. Ratio of bacterial titers right after and 6 h after infection is shown. The wild type replicated 35-fold during this time and was arbitrarily set to one. Average values and standard deviations were calculated from experiments performed in triplicate. Statistical significance is indicated by asterisks (P < 0.01, t-test with Bonferroni–Holm correction).
