BIOLOGICAL INDICATORS FOR LOW TEMPERATURE STEAM AND FORMALDEHYDE STERILIZATION - INVESTIGATION OF THE EFFECT OF CHANGE IN TEMPERATURE AND FORMALDEHYDE CONCENTRATION ON SPORES OF BACILLUS STEAROTHERMOPHILUS NCIMB 8224

摘要

Five strains of Bacillus stearothermophilus have been studied to identify a spore strain to be used as a biological indicator organism for low temperature steam and formaldehyde sterilization. Three strains gave poor reproducibility of batch size and growth index and were discarded. The other two strains gave good reproducibility with a high growth index and gave rise to linear survivor curves when exposed to 5% aqueous formaldehyde. However, only NCIMB 8224 sporulates on a simpler medium and as it was the most resistant to formaldehyde, it was further studied. Tests were carried out in a modified miniclave and factors studied included temperature of the steam and formaldehyde concentration. Al studies confirmed the suitability of this strain as a biological indicator organism.