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Differential damage in bacterial cells by microwave radiation on the basis of cell wall structure
1Department of Food Science and Technology, Kyungpook National University, Taegu, Korea.
Abstract:
Microwave radiation in Escherichia coli and Bacillus subtilis cell suspensions resulted in a dramatic reduction of the viable counts as well as increases in the amounts of DNA and protein released from the cells according to the increase of the final temperature of the cell suspensions. However, no significant reduction of cell density was observed in either cell suspension. It is believed that this is due to the fact that most of the bacterial cells inactivated by microwave radiation remained unlysed. Scanning electron microscopy of the microwave-heated cells revealed severe damage on the surface of most E. coli cells, yet there was no significant change observed in the B. subtilis cells. Microwave-injured E. coli cells were easily lysed in the presence of sodium dodecyl sulfate (SDS), yet B. subtilis cells were resistant to SDS.
Insights
Microwave radiation significantly reduced viable bacterial counts and increased DNA/protein release in *Escherichia coli* and *Bacillus subtilis* suspensions. Most inactivated cells remained intact, with *E. coli* showing surface damage and SDS sensitivity, unlike *B. subtilis*.
Area of Science:
- Microbiology
- Biophysics
- Food Science
Background:
- Bacterial inactivation is crucial for food safety and sterilization.
- Understanding the physical effects of microwave radiation on bacterial cells is essential for optimizing its application.
- Different bacterial species may exhibit varying sensitivities to microwave treatment.
Purpose of the Study:
- To investigate the impact of microwave radiation on the viability and cell integrity of *Escherichia coli* and *Bacillus subtilis*.
- To analyze the physical changes in bacterial cells post-microwave exposure.
- To assess the susceptibility of microwave-treated cells to lysis.
Main Methods:
- Exposure of *Escherichia coli* and *Bacillus subtilis* cell suspensions to microwave radiation.
- Measurement of viable cell counts, released DNA, and protein.
- Cell density analysis.
- Scanning electron microscopy (SEM) for surface morphology.
- Sodium dodecyl sulfate (SDS) lysis assay.
Main Results:
- Microwave radiation dose-dependently reduced viable cell counts and increased DNA/protein release, correlated with final temperature.
- No significant reduction in cell density was observed, indicating cell inactivation without lysis.
- SEM revealed surface damage on *E. coli* but not *B. subtilis*.
- *E. coli* cells were easily lysed by SDS, while *B. subtilis* cells were resistant.
Conclusions:
- Microwave radiation effectively inactivates *E. coli* and *B. subtilis* but primarily through non-lytic mechanisms.
- *E. coli* exhibits greater susceptibility to microwave-induced surface damage and subsequent SDS lysis compared to *B. subtilis*.
- The findings highlight differential responses of bacterial species to microwave treatment, impacting sterilization efficacy.