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Bacterial cells exposed to nanosecond pulsed electric fields show lethal and sublethal effects
S Perni1, P R Chalise, G Shama
1Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK.
International Journal of Food Microbiology
|November 21, 2007
Summary
High-intensity, nanosecond electrical pulses significantly reduce Escherichia coli and Salmonella typhimurium populations. Most survivors exhibit sublethal injury, indicating an accumulation of damage rather than an immediate death mechanism.
Area of Science:
- Microbiology
- Biophysics
- Food Safety
Background:
- Bacterial inactivation is crucial for food safety and public health.
- Electrical pulse technologies offer non-thermal methods for microbial control.
Purpose of the Study:
- To investigate the efficacy of nanosecond electrical pulses in inactivating Escherichia coli and Salmonella typhimurium.
- To characterize the injury mechanisms and survival kinetics of bacteria exposed to electrical pulses.
Main Methods:
- Bacterial cell suspensions (E. coli K12, S. typhimurium) were treated with 32 ns electrical pulses at 100 kV/cm.
- Cells were cultured on Tryptone Soya Agar (TSA) with varying NaCl concentrations (3-5% w/v).
- Colony counts were monitored over 3 days to assess inactivation and injury.
Main Results:
- A 2 log(10) reduction in E. coli and a 1 log(10) reduction in S. typhimurium were observed.
- Only 1% of surviving cells were uninjured; sublethal injury increased with treatment.
- Sublethal injury prolonged the lag phase of bacterial growth, suggesting cumulative damage.
Conclusions:
- Nanosecond electrical pulses are effective in reducing viable bacterial populations.
- Bacterial inactivation by electrical pulses involves sublethal injury accumulation, not an 'all-or-nothing' process.
- Further research into the mechanisms of nanosecond pulse inactivation is warranted.
