Fig. 2
ST398 CA-MRSA virulence in a mouse model. The seven ST398 CA-MRSA isolates were compared with closely related ST398 MSSA, all ST398 LA-MSSA obtained for this study, and representative Chinese ST5 and ST239 HA-MRSA strains by in vivo analysis of virulence. In addition, two USA300 CA-MRSA strains (SF8300, LAC) and the genome-sequenced LA-MRSA S0385 standard strain were used in the comparisons. Isolate selection for the MSSA and HA-MRSA groups was performed, as in a previous study [26], by selecting isolates whose average PSM production was similar to that of the entire group and thus reflects the average virulence potential. Notably, for the in vivo infection studies, the ST398 CA-MRSA, MSSA, and ST5/ST239 HA-MRSA isolates were obtained from the corresponding type of human infection (respiratory and skin infection, respectively). See Additional file 1: Table S2 for isolates that were compared and their characteristics. a Mouse skin infection model. Mice received 107 live S. aureus or PBS alone in the right flank by subcutaneous injection. Skin abscesses (length × width) were measured 48 h after infection. b Mouse lung infection model. We pipetted 4 × 109 CFU/40 μl S. aureus into the nares of the anesthetized mice. All mice were euthanized 48 h after inoculation and CFU in the lung tissue were determined. a, b Three mice were infected with each strain; the shown symbols represent the average value obtained from three mice. c–f Inflammatory cytokine expression in ST398 CA-MRSA isolates in comparison. The inflammatory cytokines TNF-α and IL-6 were determined in skin (c, d) or lung tissue (e, f). a–f Statistical analysis is by one-way ANOVA with Dunnett’s post test versus the ST398 CA-MRSA group. *p < 0.05, **p < 0.01,N.S. not significant (p ≥ 0.05), # not included in the ANOVA as there is only one value