Methicillin resistant Staphylococcus aureus (MRSA) constitute a serious health care problem worldwide. This study addresses the effect of β-lactam treatment on the ability of clinically relevant MRSA strains to induce IL-12 and IL-23. MRSA strains induced a dose-dependent IL-12 response in murine bone-marrow-derived dendritic cells that was dependent on endocytosis and acidic degradation. Facilitated induction of IL-12 (but not of IL-23) called for activation of the MAP kinase JNK, and was suppressed by p38. Compromised peptidoglycan structure in cefoxitin-treated bacteria – as denoted by increased sensitivity to mutanolysin -caused a shift from IL-12 towards IL-23. Moreover, cefoxitin treatment of MRSA led to a p38 MAPK-dependent early up-regulation of Dual Specificity Phosphatase (DUSP)-1. Compared to common MRSA, characteristics associated with a persister phenotype increased intracellular survival and upon cefoxitin treatment, the peptidoglycan was not equally compromised and the cytokine induction still required phagosomal acidification. Together, these data demonstrate that β-lactam treatment changes the MRSA-induced IL-12/IL-23 pattern determined by the activation of JNK and p38. We suggest that accelerated endosomal degradation of the peptidoglycan in cefoxitin-treated MRSA leads to an early expression of DUSP-1 and accordingly, a reduction in the IL-12/IL-23 ratio in dendritic cells. This may influence the clearance of S. aureus.
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