Background: Staphylococcus aureus (S. aureus) is one of the primary causes of bone infections which are often\nchronic and difficult to eradicate. Bacteria like S. aureus may survive upon internalization in cells and may be\nresponsible for chronic and recurrent infections. In this study, we compared the responses of a phagocytic cell\n(i.e. macrophage) to a non-phagocytic cell (i.e. osteoblast) upon S. aureus internalization.\nResults: We found that upon internalization, S. aureus could survive for up to 5 and 7 days within macrophages\nand osteoblasts, respectively. Significantly more S. aureus was internalized in macrophages compared to osteoblasts\nand a significantly higher (100 fold) level of live intracellular S. aureus was detected in macrophages compared to\nosteoblasts. However, the percentage of S. aureus survival after infection was significantly lower in macrophages\ncompared to osteoblasts at post-infection days 1ââ?¬â??6. Interestingly, macrophages had relatively lower viability in\nshorter infection time periods (i.e. 0.5-4 h; significant at 2 h) but higher viability in longer infection time periods\n(i.e. 6ââ?¬â??8 h; significant at 8 h) compared to osteoblasts. In addition, S. aureus infection led to significant changes in\nreactive oxygen species production in both macrophages and osteoblasts. Moreover, infected osteoblasts had\nsignificantly lower alkaline phosphatase activity at post-infection day 7 and infected macrophages had higher\nphagocytosis activity compared to non-infected cells.\nConclusions: S. aureus was found to internalize and survive within osteoblasts and macrophages and led to\ndifferential responses between osteoblasts and macrophages. These findings may assist in evaluation of the\npathogenesis of chronic and recurrent infections which may be related to the intracellular persistence of bacteria\nwithin host cells.
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