Figure 5
Time-kill assays for ATCC 17978, AB1026, AB1027, and AB1028 with 0.25 μ g/mL (A) and 0.5 μ g/mL (B) tigecycline. In the presence of 0.25 μg/mL tigecycline, all tested strains showed similar surviving colony forming unit (CFU) curves, in which the lowest value occurred at 4 h and was followed by regrowth. AB1026 had a greater CFU reduction than the wild-type strain throughout the assay period, which could be restored by baeR reconstitution. Increasing the tigecycline concentration to 0.5 μg/mL resulted in a marked 4.7-log10 CFU reduction for AB1026 at 8 h, which was followed by regrowth, whereas a smaller reduction was observed for the wild-type strain. baeR reconstitution did not fully restore the ability of AB1026 to resist 0.5 μg/mL tigecycline. AB1028 had a slight, though not significant, CFU reduction compared to the wild-type strain in the presence of 0.25 or 0.5 μg/mL tigecycline. Viable counts represented by CFUs were determined at time 0 and at 4, 8, 12, and 16 h after inoculation. A time-kill curve was constructed for each strain. The results are displayed as the means ± SD from three independent experiments. *, P < 0.05.