Figure 2. HrtBA expression is essential for full GBS virulence.

(A) Luminescence of WT(plux) and ΔhrtBA(plux) streaked on solid agar plates. Luminescence was imaged with the IVIS 200 system (acquisition time, 1 min; binning 8) (Methods). (B) Course of infection of WT and ΔhrtBA GBS strains in mice. BALB/c mice were infected by intravenous injection of 2.10⁷ CFU of luminescent WT(plux) and ΔhrtBA(plux) GBS strains. Light emission in whole anesthetized animals was acquired and imaged in an IVIS 200 imaging system (acquisition time, 10 min; binning 8) immediately following bacterial inoculation (t = 0), at 8 h and 13 h (Methods). Batches of 3 mice for each time are shown and are representative of 3 independent experiments. (C) Quantification of bioluminescence in live mice at 8 h and 13 h post-infection with WT(plux) and ΔhrtBA(plux) as described in (B). Images were analyzed by measuring the total light flux (number of photons per second). Light emission from mice at 0 time point was subtracted. Box and whiskers plot of data from 5 experiments (corresponding to n = 15 mice per time point per strain). Quantified luminescence values correlate with bacterial counts in different organs (e.g., Fig. 3A). Two-tailed Mann–Whitney analyses was usedto determine P values: 8 h, P = 0.015; 13 h, P = 0.006. *P < 0.05 and ***P < 0.001 according to the Mann–Whitney test.