Metal resistant bacteria on gold particles: Implications of how anthropogenic contaminants could affect natural gold biogeochemical cycling.

In Earth's near-surface environments, gold biogeochemical cycling involves gold dissolution and precipitation processes, which are partly attributed to bacteria. These biogeochemical processes as well as abrasion (via physical transport) are known to act upon gold particles, thereby resulting in particle transformation including the development of pure secondary gold and altered morphology, respectively. While previous studies have inferred gold biogeochemical cycling from gold particles obtained from natural environments, little is known about how metal contamination in an environment could impact this cycle. Therefore, this study aims to infer how potentially toxic metal contaminants could affect the structure and chemistry of gold particles and therefore the biogeochemical cycling of gold. In doing so, river sediments and gold particles from the De Kaap Valley, South Africa, were analysed using both microanalytical and molecular techniques. Of the metal contaminants detected in the sediment, mercury can chemically interact with gold particles thereby directly altering particle morphology and "erasing" textural evidence indicative of particle transformation. Other metal contaminants (including mercury) indirectly affect gold cycling by exerting a selective pressure on bacteria living on the surface of gold particles. Particles harbouring gold-tolerant bacteria with diverse metal resistant genes, such as Arthrobacter sp. and Pseudomonas sp., contained nearly two times more secondary gold relative to particles harbouring bacteria with less gold-tolerance. In conclusion, metal contaminants can have a direct or indirect effect on gold biogeochemical cycling in natural environments impacted by anthropogenic activity.

Efficacy and acceptability of the new oral phosphate binder Lenziaren(®) in healthy cats fed a renal diet.

The efficacy and acceptability of the new oral phosphate binder Lenziaren(®) (SBR759) were evaluated in healthy cats fed with a commercial diet containing low amounts of phosphate ('renal diet'). Lenziaren(®) at 0.125, 0.25, 0.5 and 1 g/day was compared to a reference product Lantharenol(®) (3.0 g/day) and a placebo in a masked, randomized, parallel-group design study in 36 cats (n = 6 per group). All products were mixed with the ration which was fed once daily for 28 days. Lenziaren(®) produced significant dose-related reductions in serum and urine phosphate concentrations, faecal apparent phosphorus digestibility and fractional urinary phosphate excretion. Cats administered Lenziaren(®) consumed significantly less food than the placebo group, but this had no negative impact on body weight or acceptability assessments. When compared to the positive control, Lantharenol(®) , Lenziaren(®) was significantly more acceptable (0.125, 0.5 and 1.0 g/day doses), was associated with higher food consumption (0.125, 0.5 and 1.0 g/day doses) and had greater efficacy in reducing serum phosphate (0.5 and 1.0 g/day) and urine phosphate concentrations (1.0 g/day). In conclusion, Lenziaren(®) was an effective oral phosphate binder in healthy cats fed with a renal diet. Lenziaren(®) was well accepted and tolerated. Dosages of 0.25-1.0 g/cat per day are recommended for clinical testing.

Katkor cat litter, a non-invasive method of collecting cat urine for phosphate determination.

This study was done to compare the collection of cat urine, for phosphate concentration determination, by catheterisation with that via a proprietary cat litter (Katkor). The passage of urine through the litter or its retention in the litter for a period of 2 hours did not affect the concentration of phosphates compared with that of the original sample. Apart from a small volume of urine trapped in the litter by capillary action, and some urine adhering to the funnel in which the litter was placed, the litter proved to be an excellent medium for routine urine collection from cats, and more especially as an alternative to catheterisation when regular collection from a particular cat is required.

The use of fractal analysis to reveal remodelling in human alveolar bone following the placement of dental implants.

In order to confirm the presence of adequate bone support for implants it is necessary to examine the surrounding bone at intervals. While this may be attempted by looking for changes in serial radiographs, such comparisons are inaccurate unless standardized procedures are followed which allow subtraction of consecutive digital images. As image textures are less susceptible to magnification distortion, it was decided to examine the fractal dimensions of successive radiographs of bone after implant placement. All available panoramic radiographs for each of 18 patients who had received fixed implant-supported prostheses were digitized. A window of bone adjacent and distal to the most posterior implant was defined as the region of interest; the fractal dimension of the image was calculated. Linear regression was used to investigate whether there were any significant shifts in fractal dimension during the recall period after implantation. A significant increase in fractal dimension was found during the period up to 2 yr after implantation (p < 0.001). The most pronounced increase was in the region of bone around the neck of the implant. An increase in orientation of the image in a direction oblique to the implant was also found during the same period. These changes are consistent with models derived from finite-element analysis that predict the relation between trabecular architecture and strain. One subject's radiographs had a significant negative regression slope, which further monitoring may reveal was an early sign of implant failure. The satisfactory remodelling of bone in response to implant placement may be monitored using a texture analysis of routine orthopantomograms.

Effects of pulsed electromagnetic fields on rat skin metabolism.

In an attempt to approach the mechanism of action of pulsed electromagnetic fields (PEMF) on biological systems, the effects on protein synthesizing activity and on membrane transport have been examined in rat skin. PEMF characterized by specific physical parameters stimulate the incorporation of L-[U-14C]isoleucine into the proteins of rat skin as well as the alpha-amino[1-14C]isobutyric acid uptake during incubation in buffer medium with extracellular electrolyte composition. Analogous incubation experiments carried out in an intracellular medium results in an inhibitory effect of PEMF on both biological functions. Addition of 10(-3) M ouabain to the incubation medium, partially blocking the Na+/K+-ATPase pump mechanism, apart from reducing amino acid transport, results in an overall disappearance of any stimulatory effects by PEMF. PEMF applied to the skin in the presence of 10(-3) M 2,4-dinitrophenol uncoupling the oxidative phosphorylation in the mitochondria and seriously restricting protein synthesis, still provides a limited stimulatory effect on protein synthesizing activity and on membrane transport. The effects of PEMF may well be understood by an increased availability of precursor elements controlled at the cell membrane level. Indeed the observed effects may even be simulated outside electromagnetic fields by modifications in the electrolyte composition of the incubation medium.

Conservative treatment of ipsilateral supracondylar femoral fracture after total knee arthroplasty.

Conservative as well as operative treatment has been proposed for fractures above a knee prosthesis. Three cases are reported and an explanation for the fractures on a mechanical basis is given. Our results shows that closed treatment also leads to satisfactory results, avoiding the risks of extensive surgery.

The mechanical characteristics of cancellous bone at the upper femoral region.

Mechanical behaviour of trabecular bone at the upper femoral region of human bones has been studied by compression tests on trabecular bone specimens removed from normal femora obtained at autopsy. Compression tests were performed along three different axes of loading on wet specimens and high loading rates. Femoral head specimens proved to be the strongest for any axis of loading. Large variation in compressive strength and modulus of elasticity is seen within and between femoral bone samples. Anisotropy and differences in anisotropy for the different regions have been observed. A significant correlation between mechanical properties (sigma max - E) and bone mineral content of the specimen was found. Tests on whole bone structures demonstrate that removal of the central part of the trabecular bone at the proximal femur reduces the strength for impact loading considerably (+/- 50%).