title: Evaluation of thermal inactivation of Escherichia coli using microelectrode ion flux measurements with osmotic stress.
abstract: OBJECTIVE
  To elucidate the potential use of microelectrode ion flux measurements to evaluate bacterial responses to heat treatment.
  
  
  RESULTS
  Escherichia coli K12 was used as a test bacterium to determine whether various heat treatments (55-70°C for 15 min) affected net ion flux across E. coli cell membranes using the MIFE™ system to measure net K(+) fluxes. No difference in K(+) fluxes was observed before and after heat treatments regardless of the magnitude of the treatment. Applying hyperosmotic stress (3% NaCl w/v) during flux measurement led to a net K(+) loss from the heat-treated E.coli cells below 65°C as well as from nonheated cells. In contrast, with E. coli cells treated at and above 65°C, hyperosmotic stress disrupted the pattern of K(+) flux observed at lower temperatures and resulted in large flux noise with random scatter. This phenomenon was particularly apparent above 70°C. Although E. coli cells lost the potential to recover and grow at and above 62°C, K(+) flux disruption was not clearly observed until 68°C was reached.
  
  
  CONCLUSIONS
  No changes in net K(+) flux from heat-stressed E. coli cells were observed directly as a result of thermal treatments. However, regardless of the magnitude of heat treatment above 55°C, loss of viability indicated by enrichment culture correlated with disrupted K(+) fluxes when previously heated cells were further challenged by imposing hyperosmotic stress during flux measurement. This two-stage process enabled evaluation of the lethality of heat-treated bacterial cells within 2 h and may be an alternative and more rapid method to confirm the lethality of heat treatment.
  
  
  CONCLUSIONS
  The ability to confirm the lethality of thermal treatments and to specify minimal time/temperature combinations by a nonculture-dependent test offers an alternative system to culture-based methods.
authors.affiliation: Tasmanian Institute of Agricultural Research, School of Agricultural Science, University of Tasmania, Tasmania, Australia. koseki@affrc.go.jp
authors.forename: S
authors.initials: S
authors.lastname: Koseki
authors.forename: M L
authors.initials: ML
authors.lastname: Tamplin
authors.forename: J P
authors.initials: JP
authors.lastname: Bowman
authors.forename: T
authors.initials: T
authors.lastname: Ross
authors.forename: T A
authors.initials: TA
authors.lastname: McMeekin
mesh_terms: D048168:Escherichia coli K12 / Q000254:growth & development / Q000502:physiology*; D006358:Hot Temperature; D007477:Ions / Q000032:analysis*; D050296:Microbial Viability; D008839:Microelectrodes; D009995:Osmosis; D011188:Potassium / Q000032:analysis; D013312:Stress, Physiological
chemical_list: D007477:Ions; D011188:Potassium