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Evaluation of thermal inactivation of Escherichia coli using microelectrode ion flux measurements with osmotic stress
Author(s) -
Koseki S.,
Tamplin M.L.,
Bowman J.P.,
Ross T.,
McMeekin T.A.
Publication year - 2012
Publication title -
letters in applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.698
H-Index - 110
eISSN - 1472-765X
pISSN - 0266-8254
DOI - 10.1111/j.1472-765x.2011.03194.x
Subject(s) - escherichia coli , microelectrode , osmotic shock , flux (metallurgy) , ion , enterobacteriaceae , stress (linguistics) , chemistry , biophysics , microbiology and biotechnology , biology , chromatography , biochemistry , electrode , gene , organic chemistry , linguistics , philosophy
Aims: To elucidate the potential use of microelectrode ion flux measurements to evaluate bacterial responses to heat treatment. Methods and 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. Significance and Impact of the Study: 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.