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

Five strains of Bacillus stearothermophilus have been studied to ident ify a spore strain to be used as a biological indicator organism for l ow temperature steam and formaldehyde sterilization. Three strains gav e poor reproducibility of batch size and growth index and were discard ed. The other two strains gave good reproducibility with a high growth index and gave rise to linear survivor curves when exposed to 5% aque ous formaldehyde. However, only NCIMB 8224 sporulates on a simpler med ium and as it was the most resistant to formaldehyde, it was further s tudied. Tests were carried out in a modified miniclave and factors stu died included temperature of the steam and formaldehyde concentration. Al studies confirmed the suitability of this strain as a biological i ndicator organism.