Staphylococcus aureus metal activation

In microbes without a permeability barrier, or when the barrier fails, a mechanism must be in place to export metals from the cytoplasm. These active transport systems involve energy-dependent, membrane-bound efflux pumps that can be encoded by either chromosomal- or plasmid-borne genes. Active transport is the most well-studied metal resistance mechanism. Some of these include the ars operon for exporting arsenic from E. coli, the cad system for exporting cadmium from Staphylococcus aureus, and the cop operon for removing excess copper from Enterococcus hiraeP i9A0... 

Mn2+ active transport system in Staphylococcus aureus. These metal-microbe interactions result in decrease microbial growth, abnormal morphological changes, and inhibition of biochemical processes in individual (Akmal et al. 2005a,b). The toxic effects of metals can be seen on a community level as well. In response to metal toxicity, overall community numbers and diversity decrease. Soil is a living system where all biochemical activities proceed through enzymatic processes. Heavy metals have also adverse effects on enzyme activities (Fig. 1). 

For example, NmtR from Mycobacterium tuberculosis is a member of the ArsR/SmtB family that responds in vivo to nickel, and to a lesser extent to cobalt, which binds in an a5 site. Zinc is a poor allosteric inducer both in vitro and in vivo, even though it binds more tightly to the protein than nickel and cobalt (38). An explanation for these observations was provided by spectroscopic analysis that revealed the Zn(II) ion bound in a tetrahedral 4-coordinate site, whereas Ni(II) was bound in a 6-coordinate octahedral site (38, 39). In contrast, CzrA from Staphylococcus aureus responds well to zinc, not nickel, but this protein binds the different metal ions in an a5 site with the same type of geometries as in NmtR (39). Thus, these two proteins accommodate each metal ion in the preferred coordination geometries of the metals, but they have evolved such that only one activates the allosteric response of each protein 4-coordinate activates CzrA and 6-coordinate activates NmtR. 

A wide variety of natural and synthetic materials have been used for biomedical applications. These include polymers, ceramics, metals, carbons, natural tissues, and composite materials (1). Of these materials, polymers remain the most widely used biomaterials. Polymeric materials have several advantages which make them very attractive as biomaterials (2). They include their versatility, physical properties, ability to be fabricated into various shapes and structures, and ease in surface modification. The long-term use of polymeric biomaterials in blood is limited by surface-induced thrombosis and biomaterial-associated infections (3,4). Thrombus formation on biomaterial surface is initiated by plasma protein adsorption followed by adhesion and activation of platelets (5,6). Biomaterial-associated infections occur as a result of the adhesion of bacteria onto the surface (7). The biomaterial surface provides a site for bacterial attachment and proliferation. Adherent bacteria are covered by a biofilm which supports bacterial growth while protecting them from antibodies, phagocytes, and antibiotics (8). Infections of vascular grafts, for instance, are usually associated with Pseudomonas aeruginosa Escherichia coli. Staphylococcus aureus, and Staphyloccocus epidermidis (9). 

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