Nitrogen Dioxide Sterilization Follows Log-Linear Microbial Inactivation Kinetics Using Geobacillus...

Area of Science:

• Microbiology
• Sterilization Science
• Chemical Kinetics

Background:

• Biological indicators (BIs) are crucial for validating sterilization processes.
• Nitrogen dioxide (NO2) gas is an emerging sterilant with potential for low-temperature applications.
• Understanding the inactivation kinetics of microbial spores under NO2 exposure is essential for process development.

Purpose of the Study:

• To determine the inactivation kinetics of Geobacillus stearothermophilus spores exposed to nitrogen dioxide (NO2) gas.
• To evaluate the impact of humidity on NO2 gas sterilization efficacy.
• To establish the relationship between NO2 exposure and microbial inactivation for achieving a specific Sterility Assurance Level (SAL).

Main Methods:

• Geobacillus stearothermophilus spores on biological indicators (BIs) were exposed to NO2 gas at 80% relative humidity.
• Direct enumeration and fraction negative methods were combined to quantify surviving spores across a wide population range.
• D-values and coefficients of determination (r^2) were calculated to model inactivation kinetics.

Main Results:

• A log-linear relationship was observed between NO2 exposure and spore inactivation over an 8 log10 population range.
• High coefficients of determination (r^2 > 0.8) confirmed the reliability of the kinetic model.
• Inactivation kinetics were consistent across different BI lots and spore crops.

Conclusions:

• Nitrogen dioxide sterilization follows first-order log-linear microbial inactivation kinetics.
• The mechanism of action is consistent with a single active species, likely related to NO2's chemical properties.
• This study provides the first report on the microbial inactivation kinetics of NO2 sterilization, supporting its use for achieving SAL 10^-6.