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Selection of biological indicator for validating microwave heating sterilization
1Quality Control Department, Misato Plant, Eisai Company, Limited, Saitama, Japan.
Abstract:
For the purpose of selecting an appropriate biological indicator for evaluation of the effects of microwave heating sterilization, we examined aerobic bacterial spores to determine whether microwaves have non-thermal sterilization effects. After microwave irradiation on dry bacterial spores (three species), none of the bacterial spores were killed. The survival rate of the spores after microwave irradiation of spore suspensions (twelve species) was compared with that after heating by a conventional method. The order of heat resistance in the bacterial species was similar between the two heating methods. Bacillus stearothermophilus spores were the most heat-resistant. These results suggest that microwaves have no non-thermal sterilization effects on bacterial spores, the specific resistant spores to microwave heating, and microwave heating sterilization can be evaluated in the same way as for conventional heating sterilization. As a biological indicator for evaluation of overkill sterilization, B. stearothermophilus spores may be appropriate for microwave heating sterilization as well as steam sterilization.
Insights
Microwave heating shows no non-thermal sterilization effects on bacterial spores. Bacillus stearothermophilus spores are suitable biological indicators for microwave sterilization, similar to steam sterilization.
Area of Science:
- Microbiology
- Sterilization technologies
Background:
- Evaluating sterilization methods requires appropriate biological indicators.
- Microwave heating sterilization efficacy needs assessment for non-thermal effects.
Purpose of the Study:
- Determine if microwaves possess non-thermal sterilization effects on bacterial spores.
- Identify suitable biological indicators for microwave heating sterilization.
Main Methods:
- Irradiation of dry bacterial spores (three species) and spore suspensions (twelve species) with microwaves.
- Comparison of spore survival rates with conventional heating methods.
- Assessment of heat resistance order across different bacterial species.
Main Results:
- No bacterial spores were killed by microwave irradiation in dry form.
- Microwave heating exhibited similar heat resistance patterns to conventional heating for spore suspensions.
- Bacillus stearothermophilus spores demonstrated the highest resistance to microwave heating.
Conclusions:
- Microwaves do not exhibit non-thermal sterilization effects on bacterial spores.
- Microwave heating sterilization can be evaluated comparably to conventional methods.
- Bacillus stearothermophilus spores are appropriate biological indicators for microwave sterilization.