M. R. Wertheimer

Plasma sterilization: spore destruction by microwave plasmas

Low-pressure plasmas are now being used for sterilization at ambient temperature. In this work, we have studied the possible mechanism of spore destruction by plasma, and compare it with etching of synthetic polymers. Bacillus subtilis spores were inoculated at the bottom of special glass vials and subjected to different plasma gas compositions, all known to etch polymers. The mortality rate of spores was found to vary with gas composition, between less than a 2 log decrease in 8 minutes for a pure oxygen plasma, to a 6 log decrease with 0 2 CF 4 mixture. Examination by scanning electron microscopy (SEM) showed that spores were significantly etched after 30 minutes of plasma exposure, but not completely. We speculate about their etch resistance, compared with that of synthetic polymers, on the basis of their morphology and their complex coating structure.