Fig. 7

S. aureus infection of human leukocytes and larvae of Galleria mellonella. A Leukocyte infection with the six S. aureus study isolates. To investigate the bacterial virulence and intracellular survival after infection of leukocytes, the course of infection was followed by flow cytometry. Per experiment, the percentage of living cells post-infection was measured compared to the uninfected control. B Living GFP + and GFP − granulocytes following S. aureus infection. GFP + granulocytes indicate the portion of the granulocyte population containing intracellular GFP-expressing S. aureus, and GFP − indicates the population that remained uninfected. Cells were infected with S. aureus for 30 min and subsequently incubated for 30 min with lysostaphin to remove non-internalized bacteria. C Virulence profile of the six S. aureus study isolates in G. mellonella. To investigate their virulence, three independent G. mellonella infection experiments were performed. Per experiment, each strain was used to inoculate 15 G. mellonella larvae (45 larvae/strain in total). Each individual larva was inoculated with 10 μl aliquots of a diluted bacterial suspension (1 × 10.⁸ CFU/ml) of the respective S. aureus strain. Larval killing was assessed at 24, 48, 72, and 96 h post-inoculation. All values are the mean ± the standard deviation of the three independent infection experiments. Statistical significance of observed differences in virulence between the six S. aureus study strains as assessed using a Gehan-Breslow-Wilcoxon test. *P < 0.03; **P < 0.002; ***P < 0.0002; ****P < 0.0001