The effect of different water-insoluble anorganic salts on the resistance and storage time of Bacillus stearothermophilus spores used for biological indicators.

The survival of Bacillus stearothermophilus spores was investigated over 7 years. The spores were precipitated with 18 insoluble inorganic salts. There were hydroxides, carbonates, oxalates, phosphates, and sulfate of aluminium, barium, calcium, iron, magnesium, manganese, and tin. The stability of the spores to dry and moist heat was strongest in precipitates of barium and calcium salts. Most phosphates and the heavy metals caused a rapid inactivation of spores. Finally, the survival of the spores in the 7 years of observation was the best in barium sulfate and calcium oxalate.