Socialization of Providencia stuartii enables resistance to environmental insults.

Providencia stuartii is a highly-social pathogen responsible for nosocomial chronic urinary tract infections. The bacterium indeed forms floating communities of cells (FCC) besides and prior-to canonical surface-attached biofilms (SAB). Within P. stuartii FCC, cells are riveted one to another owing to by self-interactions between its porins, viz. Omp-Pst1 and Omp-Pst2. In pathophysiological conditions, P. stuartii is principally exposed to high concentrations of urea, ammonia, bicarbonate, creatinine and to large variations of pH, questioning how these environmental cues affect socialization, and whether formation of SAB and FCC protects cells against those. Results from our investigations indicate that FCC and SAB can both form in the urinary tract, endowing cells with increased resistance and fitness. They additionally show that while Omp-Pst1 is the main gateway allowing penetration of urea, bicarbonate and ammonia into the periplasm, expression of Omp-Pst2 enables resistance to them.

Preparation and Characterization of Undoped and Chromia-Doped Porous Alumina Using Different-Sized Particles

Highly porous alumina (Al2O3) was prepared by sintering of Al2O3 powder using ammonia bicarbonate (NH4HCO3) as a pore-forming agent and chromia (Cr2O3) as a sintering additive. In order to investigate the influence of particle shape and size on the characterization of sintered porous Al2O3, the starting Al2O3 powders included commercial disk micro-sized powder and synthesized spherical nanopowder. The nanoscale Al2O3 powder was produced via combustion synthesis route. At the optimal pore-forming agent concentration, the porous Al2O3 sintered by nanoparticles had a smaller pore size and a lower total porosity than the one prepared by microparticles. The differences of open porosity and closed porosity between porous Al2O3 synthesized by micro and nano-scale powders with and without Cr2O3 dopant were also discussed. In addition, the compressive strength of porous Al2O3 achieved by nano-sized powders, especially with Cr2O3 dopant, had a higher value in comparison with the one prepared by micro-sized powders.

Effect of several natural water constituents on bromate formation during ozonation

Synthetic water matrices containing ammonia, bicarbonate, hydrogen peroxide, and natural organic matter were studied to identify the effects of these compounds (individually and in combination) on bromate formation. Ammonia alone was observed to significantly reduce bromate formation through the sequestering of brominated intermediates as bromamines. Natural organic matter reacted quickly with bromamines, which could impair the ability of ammonia to block bromate formation. Bicarbonate was observed to generally promote bromate formation in otherwise pure water, but bicarbonate worked synergistically with ammonia to reduce bromate formation by a greater factor than ammonia alone, due to OH radical scavenging. Experiments showed that hydrogen peroxide lowered the effectiveness of ammonia to block bromate formation.

The Interrelations of Faecal Ammonia, pH and Bicarbonate: Evidence of Colonic Absorption of Ammonia by Non-Ionic Diffusion

1. Ammonia, bicarbonate and pH were measured in samples of faecal dialysate from thirteen healthy subjects taking free diets. To observe the effect of marked changes in faecal pH, three subjects were also studied while taking 25 mmol/day of MgCO3 or Na2SO4 by mouth. Both salts increased stool weight without causing diarrhoea, but stool pH was significantly increased by MgCO3 and decreased by Na2SO4. 2. The total ammonia concentration and pH of faecal dialysate were very variable, but showed a highly significant negative correlation similar to that already established in man between urinary excretion of ammonia and urine pH. This relationship was more marked when individual subjects were studied while faecal pH was deliberately varied by administration of MgCO3 and Na2SO4. 3. Faecal bicarbonate concentrations were positively correlated with pH. Faecal Pco2 was usually in the range 40–120 mmHg, the higher Pco2 values being found in the more acid samples. Faecal total ammonia concentrations were negatively correlated with faecal bicarbonate. 4. These findings suggest that passive non-ionic diffusion is the main mechanism by which ammonia is absorbed by the colon, but do not exclude a minor contribution from diffusion of ionized ammonium. Colonic secretion of bicarbonate facilitates non-ionic diffusion of ammonia by providing an anion which is also absorbed by non-ionic diffusion, so maintaining an alkaline intraluminal reaction that continues to generate unionized ammonia.

Relation of the Saluresis of Urea and Mannitol Loading to the Normal Excretion of Electrolyte

In hydrated dogs subjected to mild solute diuresis with mannitol and urea, the patterns of change in the course of the experiments in the ratios of sodium and chloride excretion to total solute excretion were not significantly different from those observed in control experiments conducted in an identical manner but in which no solute load was imposed. In hydrated, mildly acidotic dogs a similar result was obtained if only the mean values of the data are considered; in individual experiments loading produced considerable fluctuations in the ratios as compared with control experiments. Hydropenic animals, on the other hand, showed an increase in the sodium:total solute ratio with loading but the chloride:total solute ratio was not significantly affected. The potassium: total solute ratio was, in general, also independent of solute diuresis. In the hydropenic and hydrated acidotic animals the ratio was unaffected by loading but in the hydrated nonacidotic animals, considerable variability in excretion made interpretation of the ratios difficult. Ratios calculated in a similar manner for titratable acid, ammonia, bicarbonate and phosphorus all fell with loading. Reductions in filtration rate occasioned by urea loading had no effect on the ratios for sodium, potassium and chloride. The data appear to provide a link between the saluresis of solute loading and the normal excretion of electrolyte and suggest that the saluresis is simply a magnified operation of the normal mechanism concerned with electrolyte. The ratio of electrolyte to total solute would appear to be of physiological significance, differing from other parameters of electrolyte excretion in that it is independent of at least moderate fluctuations in the rate of nonelectrolyte excretion.