Nitriding of AISI 316L surgical stainless steel in fluidized bed reactor

In this study, the effect of nitriding on some properties of surgical AISI 316L stainless steel was investigated. Nitriding heat treatment was carried out in a fluidized bed reactor at a temperature of 560 C for 16 h. The hardness of nitrogen-rich region just below the coated layer was around 1200 DPN. Nitrides (CrN, Fe4N and Fe2-3N) formed on the surface was confirmed by XRD analysis. Microstructural changes were observed by optical microscopy. The microstructure of nitrided specimens showed a white layer at the top consisting of iron nitride and chromium nitride. The hardness of nitrided specimens decreased with distance from the surface to the interior of the test sample. Scanning electron microscope study combined with energy dispersive X-ray spectroscopy showed the presence of nitrogen in the outer layer and the transition layer, but not in the base metal. (C) 2004 Elsevier Ltd. All rights reserved

Multidrug Efflux in the Context of Two-Membrane Cell Envelopes

The trans-envelope drug efflux in Gram-negative bacteria demands assembly of specialized protein complexes that in addition to inner membrane transporters include periplasmic membrane fusion proteins and outer membrane channels due to the presence of a double membrane. These complexes are highly versatile and constitute a major antimicrobial resistance mechanism of Gram-negative bacteria. The modular organization of the tripartite assemblies in Gram-negative bacteria allows them to accommodate a wide array of multidrug efflux transporters enabling efflux across both the inner and the outer membranes of the cell envelope. This chapter focuses on the structures and mechanisms of trans-envelope multidrug efflux pumps from Gram-negative bacteria. We summarize the current state of the field and the emerging model for multidrug efflux in the context of two membranes