TNF and osteomyelitis: In line with previously published data showing the inductive effects of S. aureus with regard to the expression of pro-inflammatory cytokines in different cell types [62,63] including osteoblasts [28], we found that the most persistent and at the same time most toxic strain, ST239, was able to strongly increase the expression levels of IL-6 and TNF-α, two cytokines often over-expressed during the development and progression of osteomyelitis [64,65,66,67] at both 3 and 24 h p.i. compared with other strains.