title: Bacterial cells exposed to nanosecond pulsed electric fields show lethal and sublethal effects.
abstract: Cell suspensions of Escherichia coli K12 and Salmonella typhimurium were exposed to electrical pulses of 32 ns duration at a field intensity of 100 kV/cm and a repetition rate of 30 pulses per second for a total of 300 s. Treated cells were plated onto Tryptone Soya Agar (TSA) and TSA supplemented with NaCl, and cell counts were monitored daily for 3 days. The concentrations of NaCl used were 3 and 4% (w/v) for E. coli and 4 and 5% (w/v) for S. typhimurium. Treatment under these conditions resulted in a 2 log(10) reduction for E. coli and approximately a single log(10) reduction for S. typhimurium. For both species of bacteria it was discovered that the surviving population was composed of only 1% of uninjured cells. Moreover, the proportion of sublethally injured cells increased more rapidly than the total recoverable population suggesting a process of injury accumulation culminating in death rather than an 'all or nothing' mechanism. Sublethal injury manifested itself in a proportion of the injured population of both species by an extended lag phase at longer treatment times. Finally, possible mechanisms by which nanosecond electric pulses inactivate bacteria are discussed.
authors.affiliation: Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK.
authors.forename: S
authors.initials: S
authors.lastname: Perni
authors.forename: P R
authors.initials: PR
authors.lastname: Chalise
authors.forename: G
authors.initials: G
authors.lastname: Shama
authors.forename: M G
authors.initials: MG
authors.lastname: Kong
mesh_terms: D015169:Colony Count, Microbial; D004558:Electric Stimulation / Q000379:methods*; D048168:Escherichia coli K12 / Q000254:growth & development / Q000502:physiology*; D005506:Food Contamination / Q000517:prevention & control; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D012486:Salmonella typhimurium / Q000254:growth & development / Q000502:physiology*; D013997:Time Factors