The microbiological tests have been carried out according to thecount-reduction test (CRT) (VDMA, 2008). As test samples, B.atrophaeus spores inoculated on aluminum strips were used. Theinitial bacterial count was on average at 2.04*106 cfu (colonyforming units) per strip. After exposure to the sterilising gas, thetest strips have been stored in 10 ml Ringer's solution. Afterwards,the spores were stripped off the aluminium strip in an ultrasonicbath and plated on nutrient agar. To ensure that a countablenumber of bacterial colonies (<300) are grown on the agar plates,several dilutions of the spore suspension have been prepared priorto the plating. The inoculation time of the plates was 24 h at 37 C.For each setting of the machine parameters, ten microbiologicalsamples have been taken. According to the CRT, the LCR can becalculated as follows:
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