Date of Award

Spring 2007

Document Type


Degree Name

Master of Science (MS)


Dental Hygiene


Dental Hygiene

Committee Director

Gayle McCombs

Committee Member

Mournir Laroussi

Committee Member

Wayne Hynes

Committee Member

Lynn Tolle

Call Number for Print

Special Collections LD4331.D46 M67 2007


Non-equilibrium atmospheric pressure plasma, also known as cold plasma, is a state of matter that consists of a mix of neutral and charged particles. Plasma generates chemically reactive species and ultraviolet radiation making them useful in decontamination applications (Kong & Laroussi, 2003). Research regarding the inactivation of gram-positive bacteria, such as Bacillus atrophaeus, by cold plasma has been studied by Laroussi et al. (2003); however, there is limited research regarding the germicidal effectiveness of cold plasma on the microorganisms Geobacillus stearothermophilus and Bacillus cereus. The purpose of this study was to determine if cold plasma technology inactivates heat resistant microorganisms, specifically, G. stearothermophilus and B. cereus vegetative cells and spores. Methods: The study consisted of 762 G. stearothermophilus and B. cereus samples exposed to cold plasma at various times and 219 control samples (N=981). Bacteria were inoculated and exposed to either indirect or direct cold plasma, incubated for 12 to 16 hours and number of colony forming units (CFU) determined. The percentage kill and log concentration reductions were computed utilizing the CFU and data was analyzed using one-way ANOVA, Kruskal Wallis and Tukey's tests at the .05 level. Results: There was a statistically significant difference in the inactivation of G. stearothermophilus vegetative cells receiving indirect exposure (p=.0001) and direct exposure (p=.0013) and B. cereus vegetative cells and spores exposed to indirect and direct cold plasma (p=.0001 for both). Cold plasma exposure to G. stearothermophilus spores demonstrated no statistically significant difference in inactivation of microorganisms receiving indirect (p=.7208) and direct (p=.0835) exposure. Conclusion: Results indicate that indirect and direct cold plasma exposure significantly inactivated G. stearothermophilus vegetative cells and B. cereus vegetative cells and spores; however, G. stearothermophilus spores were not significantly inactivated; therefore, sterility was not achieved.


In Copyright. URI: This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).