Microbiological efficacy of superheated steam - I. Communication: Results with spores of Bacillus subtilis and Bacillus stearothermophilus and with spore earth

For the spores of Bacillus subtilis and Bacillus stearothermophilus as well as for spore earth (ace. DIN 58946 Part 4 of August 1982), the dependence of resistance on the superheating of the steam used to kill germs was deter mined. A material (glass fibre fleece) was used as the germ carrier which d oes not superheat on contact with steam. The temperature of the saturated s team was 100 degrees C (B. subtilis) and 120 degrees C (B, stearothermophil us and spore earth). The yardstick for the resistance of the spores or bioi ndicators was the exposure period of the saturated or superheated steam at which 50% of the treated test objects no longer showed any viable test germ s. The spores of Bacillus subtilis were far more sensitive to superheating of steam and reacted far more than the spores of Bacillus stearothermophilus a nd the germs in the spore earth. When superheating by 4 Kelvin the spores o f Bacillus subtilis were approximately 2.5 times more resistant than they w ere to saturated steam. The resistance of Bacillus stearothermophilus and s pore earth was only slightly higher up to superheating by 10 Kelvin. The sp ores of Bacillus subtilis had the highest resistance during superheating by 29 Kelvin; they were 119 times more resistant than they were to saturated steam. The resistance maximum of the spores of Bacillus stearothermophilus was at an superheating by around 22 Kelvin. However, the spores were only 4 .1 times more resistant than they were to saturated steam. When using steam to kill germs, we must expect superheated steam. This rais es the question whether the spores of Bacillus stearothermophilus, with the ir weaker reaction to; the superheating of steam, are suitable as test germ s for sterilisation with steam in all cases.