Thermal resistance of Bacillus stearothermophilus spores on strips previously treated with calcium

Moist thermal resistance parameters of spores of B. stearothermophilus ATCC 7953, inoculated in aqueous suspensions and on strips, were evaluated at 118 degrees C and 121 degrees C, by the proposed serum-bottle-mini-autoclave method. The present work studied the effect of alkaline calcium exchange-inducing storage treatments on the viability and moist heat-resistance of B. stearothermophilus spores, stored at -18 degrees C, following impregnation into filter paper strips which had been previously treated by immersion in alkaline 0.02 M calcium acetate. The thermal resistance of B. stearothermophilus spores on strip at set work conditions as biological indicator exhibited an average medium D (121 degrees C) of 1.92 min for concentrations of 10(5)-10(6) spores per strip over 360 days of storage in a freezer. The serum-bottle-mini-autoclave measuring system resulted in reasonably accurate and reproducible BIs calibration, before using them in an equipment validation program. The calcium acetate-strip system demonstrated a very high stability (Ea = 49.95 kcal/mol) to keep the spore viability and thermoresistance over steam cycles and storage. The heat activation kinetics of spores were also studied.