Characterization of Bacillus subtilis spore inactivation in low-pressure, low-temperature gas plasma sterilization processes.
OBJECTIVE
To identify structural components of Bacillus subtilis spores serving as targets for sterilization with microwave induced low-pressure, low-temperature nitrogen-oxygen plasma.


RESULTS
The inactivation of spores followed a biphasic kinetics consisting of a log-linear phase with rapid inactivation followed by a slow inactivation phase. In the course of plasma treatment, damage to DNA, proteins and spore membranes were observed by monitoring the occurrence of auxotrophic mutants, inactivation of catalase (KatX) activity and the leakage of dipicolinic acid, respectively. Spores of the wild-type strain showed the highest resistance to plasma treatment. Spores of mutants defective in nucleotide excision repair (uvrA) and small acid-soluble proteins (Delta sspA Delta sspB) were more sensitive than those defective in the coat protein CotE or spore photoproduct repair (splB). Exclusion of reactive particles and spectral fractions of UV radiation from access to the spores revealed that UV-C radiation is the most effective inactivation agent in the plasma, whereby the splB and Delta cotE mutant spores were equally and slightly less sensitive, respectively, than the wild-type spores. Finally, the extent of damages in the spore DNA determined by quantitative PCR correlated with the spore inactivation.


CONCLUSIONS
Spore inactivation was efficiently mediated by a combination of DNA damage and protein inactivation. DNA was identified to be the primary target for spore inactivation by UV radiation emitted by the plasma. Coat proteins were found to constitute a protective layer against the action of the plasma.


CONCLUSIONS
The results provide new evidence to the understanding of plasma sterilization processes. This knowledge supports the identification of useful parameters for novel plasma sterilization equipment to control process safety.
Roth
S
S
Section Food Microbiology, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany.
Feichtinger
J
J
Hertel
C
C
D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D001426:Bacterial Proteins / Q000528:radiation effects; D003080:Cold Temperature; D015169:Colony Count, Microbial; D004249:DNA Damage / Q000528:radiation effects; D050296:Microbial Viability; D008872:Microwaves; D008954:Models, Biological; D010848:Picolinic Acids; D011312:Pressure; D013171:Spores, Bacterial / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D013242:Sterilization / Q000379:methods*; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D010848:Picolinic Acids; C004860:dipicolinic acid