Effect of phosphate buffer concentration on the heat resistance of Bacillus stearothermophilus spores suspended in parenteral solutions.

The effect of various quantities of Butterfield phosphate buffer added to four parenteral solutions on the survival of Bacillus stearothermophilus spores heated at 121 degrees C was determined. The effect of the addition of phosphate buffer on spore survival varied with the parenteral solution. Spore survival was increased or decreased, depending upon the composition of the parenteral solution and the buffer concentration. The results obtained in these experiments attest to the fact that environmental factors, including the type of ions present and ionic concentration, affect the heat destruction rate of B. stearothermophilus spores. Therefore, the sterilization requirements of a product such as a parenteral solution may be affected by small changes in formulation.