Molecular basis of antibiotic multiresistance transfer in Staphylococcus aureus.

Multidrug-resistant Staphylococcus aureus infections pose a significant threat to human health. Antibiotic resistance is most commonly propagated by conjugative plasmids like pLW1043, the first vancomycin-resistant S. aureus vector identified in humans. We present the molecular basis for resistance transmission by the nicking enzyme in S. aureus (NES), which is essential for conjugative transfer. NES initiates and terminates the transfer of plasmids that variously confer resistance to a range of drugs, including vancomycin, gentamicin, and mupirocin. The NES N-terminal relaxase-DNA complex crystal structure reveals unique protein-DNA contacts essential in vitro and for conjugation in S. aureus. Using this structural information, we designed a DNA minor groove-targeted polyamide that inhibits NES with low micromolar efficacy. The crystal structure of the 341-residue C-terminal region outlines a unique architecture; in vitro and cell-based studies further establish that it is essential for conjugation and regulates the activity of the N-terminal relaxase. This conclusion is supported by a small-angle X-ray scattering structure of a full-length, 665-residue NES-DNA complex. Together, these data reveal the structural basis for antibiotic multiresistance acquisition by S. aureus and suggest novel strategies for therapeutic intervention.

Mast Cell Deficiency Limits the Development of Chronic Rhinosinusitis in Mice.

BACKGROUND: Chronic rhinosinusitis (CRS) is one of the most common chronic diseases in adults in both developing and developed countries. The etiology and pathogenesis of CRS remain poorly understood, and the disease is refractory to therapy in many patients. Mast cell activation has been demonstrated in the sinonasal mucosa of patients with CRS; however, the specific contribution of mast cells to the development and pathogenesis of this disease has not been established. OBJECTIVE: The objective of this study was to investigate the role of mast cells in the development of CRS. METHODS: C57BL/6 wild-type and C57BL/6-Kit(W-sh/W-sh) mast cell-deficient mice were immunized by intraperitoneal allergen injection and subsequent chronic low dose intranasal allergen challenges. The sinonasal phenotypes of these groups were then evaluated and compared to saline-treated controls using radiologic, histologic, and immunologic methods. RESULTS: Wild-type mice exposed to chronic intranasal allergen developed many features seen in human CRS, including mucosal thickening, cystic changes, polyp development, eosinophilia, goblet cell hyperplasia, and mast cell activation. In contrast, sinonasal pathology was significantly attenuated in mast cell-deficient mice subjected to the same chronic allergen protocol. Specifically, tissue eosinophilia and goblet cell hyperplasia were reduced by approximately 50% compared to wild-type levels. Surprisingly, none of the mast cell-deficient mice subjected to chronic allergen challenge developed cystic changes or polypoid changes in the nose or sinuses. CONCLUSIONS: These data identify a critical role for mast cells in the development of many features of a mouse model of eosinophilic CRS, suggesting that therapeutic strategies targeting mast cells be examined in humans afflicted with this disease.