Preparation and characterization of antibacterial P2O5-CaO-Na2O-Ag2O glasses.

60P2O5-20CaO-(20-x) Na2O-xAg2O and 60P2O5-30CaO-(10-x) Na2O-xAg2O glasses, x = 0, 0.5,1, and 2 mol % were prepared using normal glass melting technique. The antibacterial activity of pressed disks of powdered glass (undoped and silver-doped glass) was investigated against S.aureus, P.aeruginosa, and E.coli micro-organisms using agar disk-diffusion assays at 37 °C for 24 h. The antibacterial activity was deduced from the inhibition zone diameter (IZD), zone of no bacterial growth, measured under the stated experimental conditions. The antibacterial activity increases with the increase in IZD and vice versa. Dissolution of glass in water at 37 °C, pH changes of water during glass dissolution, and concentrations of silver ions released from silver-doped glasses into water during their dissolution were determined. An increase in the concentration of silver ions released from silver-doped glasses into water was observed with increasing time of glass dissolution and with increasing Ag2O content. The tested silver-free and silver-doped glasses demonstrated different antibacterial activity against the tested micro-organisms. For silver-free glasses, an increase in IZD was observed with the increase in the glass dissolution rate and with the decrease in pH of water. Also, the IZD showed an increase with increasing Ag2O content of silver-doped glasses.

Production of levansucrase from Bacillus subtilis NRC 33a and enzymic synthesis of levan and Fructo-Oligosaccharides.

Bacillus subtilis NRC 33a was able to produce both inducible and constitutive extracellular levansucrase, respectively, using sucrose and glucose as carbon source. The optimal production of the levansucrase was at 30 degrees C. The effect of different nitrogen sources showed that baker's yeast with 2% concentration gave the highest levansucrase activity. Addition of 0.15 g/L MgSO(4) was the most favorable for levansucrase production. The enzymic synthesis of levan was studied using 60% acetone fraction. The results indicated that high enzyme concentrations produced increasing amounts of levan, and hence conversion of fructose to levan reached 84% using 1,000 microg/ml enzyme protein. Sucrose concentration was the most effective factor controlling the molecular weight of the synthesized levan. The conversion of fructose to levan was maximal at 30 degrees C. The time of reaction clearly affected the conversion of fructose to levan, which reached its maximum productivity at 18 hours (92%). Identification of levan indicated that fructose was the building unit of levan.