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Inactivation of Lactobacillus bacteriophage PL-1 by microwave irradiation
Y Kakita1, N Kashige, K Murata
1Faculty of Pharmaceutical Sciences, School of Medicine, Fukuoka University, Japan.
Abstract:
The effect of microwave irradiation on the survival of bacteriophage PL-1, which is specific for Lactobacillus casei, was studied using a commercial 2,450 MHz microwave oven. The phages were inactivated by microwave irradiation according to almost first-order reaction kinetics. The rate of phage inactivation was not affected by the difference in the continuous or intermittent irradiation, nor by the concentrations of phages used, but was affected by the volume of phage suspensions, which prevented the loss of generated heat. Microwave irradiation of phage suspensions produced a number of ghost phages with empty heads, but fragmentation of the tail was hardly noticed. The breakage of phage genome DNA was primarily caused by the heat generated by microwave irradiation, whereas the phage DNA was not affected by the same temperature achieved by heat from outside. Thus we concluded that the phage-inactivating effect of microwave irradiation was mainly attributed to a thermal microwave effect, which was much stronger than a simple thermal exposure.
Insights
Microwave irradiation inactivates Lactobacillus casei bacteriophage PL-1 via a thermal effect, primarily damaging phage DNA. This inactivation, following first-order kinetics, is influenced by heat retention in larger volumes.
Area of Science:
- Microbiology
- Food Science
- Biophysics
Background:
- Bacteriophages are viruses that infect bacteria.
- Lactobacillus casei is a beneficial bacterium used in food production.
- Understanding bacteriophage inactivation is crucial for food safety and industrial processes.
Purpose of the Study:
- To investigate the inactivation kinetics of bacteriophage PL-1 (specific for Lactobacillus casei) under microwave irradiation.
- To elucidate the mechanisms underlying microwave-induced phage inactivation.
Main Methods:
- Exposure of bacteriophage PL-1 suspensions to microwave irradiation (2,450 MHz).
- Analysis of phage inactivation rates under varying conditions (irradiation type, phage concentration, suspension volume).
- Microscopic examination of phage morphology and DNA integrity post-irradiation.
Main Results:
- Microwave irradiation inactivated bacteriophage PL-1 following near first-order kinetics.
- Inactivation rate was independent of irradiation type (continuous/intermittent) and phage concentration.
- Suspension volume significantly affected inactivation by influencing heat loss; larger volumes showed higher inactivation.
- Microwave irradiation generated "ghost" phages (empty heads) and caused DNA breakage, primarily due to heat generated internally.
Conclusions:
- The primary mechanism of microwave-induced bacteriophage inactivation is a thermal effect.
- This thermal effect is significantly stronger than simple external thermal exposure.
- Microwave irradiation primarily damages phage DNA through internally generated heat.