Fig. 4.

Bacterial counts from mice infected with CTX-M-15WT or CTX-M-15N135D after treatment. Mice infected via intraperitoneal injection with S. typhimurium expressing either CTX-M-15WT strain (a) or the mutant strain carrying CTX-M-15N135D (b) were treated with mecillinam (Mec), cefotaxime (Ctx), or a combination of the two. PBS was used as a negative control. Bacterial counts of liver tissue (colony-forming units (CFU)/g) are shown (four mice per group). Inoculum size was 1.5 × 105 CFU/mouse. ns: not significant; *p < 0.05; **p < 0.01. Horizontal bold line denotes the median. Statistical analysis was performed using unpaired Student’s t-test. Symbols surrounded by a black border represent counts on plates with < 20 CFU (in those cases, statistical significance was calculated assuming 20 CFU/plate). One mouse infected with the mutant CTX-M-15N135D and treated with mecillinam in combination with cefotaxime cleared the infection. Data from this mouse are not plotted