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Differentiation of the effects of lethal pH and water activity: food safety implications

journal contribution
posted on 2023-05-16, 12:41 authored by Shadbolt, CT, Thomas RossThomas Ross, Thomas McMeekinThomas McMeekin
The influence of a second lethal stress (SLS) was investigated when populations of Escherichia coli M23 OR.H-were exposed to either a low water activity (aw) of 0.90 or a pH of 3.50 after 24 h at 25°C. Regardless of the initial stress, E. coli M23 OR.H- populations initially demonstrated biphasic inactivation kinetics consisting of a rapid first phase of death followed by a slower second phase. When cultures initially exposed to aw 0.90 experienced an SLS of pH 3.50, a second rapid inactivation period was observed before a subpopulation of more resistant cells emerged. This subpopulation was able to persist for approximately 50 h after imposition of the SLS. In contrast, E. coli M23 OR.H- cells first exposed to a pH of 3.50 were inactivated rapidly to levels below the limits of detection upon imposition of an SLS of aw 0.90. It is hypothesized that pH stress constitutes a large energy drain on the cell and subsequently sensitizes it to other environmental constraints requiring expenditure of metabolic energy.


Publication title

Letters in Applied Microbiology








Tasmanian Institute of Agriculture (TIA)


Blackwell Science Ltd

Place of publication

Oxford, England

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the environmental sciences

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    University Of Tasmania