Effect of gas composition on spore mortality and etching during low-pressure plasma sterilization

The aim of this work was to investigate possible mechanisms of sterilizatio n by low-temperature gas plasma: spore destruction by plasma is compared wi th etching of synthetic polymers. Bacillus subtilis spores were inoculated at the bottom of glass vials and subjected to different plasma gas composit ions (O-2, O-2,/Ar, O-2/H-2 CO2 and O-2/CF4), all known to etch polymers. O -2/CF4 plasma exhibited much higher efficacy than all other gases or gas mi xtures tested, with a more than 5 log decrease in 7.5 min, compared with a 2 log decrease with pure oxygen. Examination by scanning electron microscop y showed that spores were significantly etched after 30 min of plasma expos ure, but not completely. We speculate about their etch resistance compared with that of synthetic polymers on the basis of their morphology and comple x coating structure. In contrast to so-called in-house plasma, sterilizatio n by Sterrad(R) tended to increase the observed spores' size; chemical modi fication (oxidation), rather than etching, is believed to be the sterilizat ion mechanism of Sterrad(R). (C) 2000 John Wiley & Sons, Inc. J Biomed Mate r Res, 51, 128-135, 2000.