Dynamics of Escherichia coli at elevated temperatures: effect of temperature history and medium

Abstract

Aims: The dynamics of Escherichia coli near the maximum temperature for growth in a rich medium are analysed. The effects of temperature history, medium composition and physiological state of the inoculum are evaluated.

Methods and results: Kinetics of E. coli K12 MG1655 is studied in 'brain-heart infusion' broth in a temperature controlled environment. Based on viable counts, 'smooth' growth curves are observed at 40, 41, 42 and 43 degrees C. The exponential growth phase at 44 and 45 degrees C is interrupted. At 46 degrees C, a period of exponential growth is followed by inactivation. Neither the physiological state of the inoculum nor medium enrichment alters the dynamics, whilst temperature pre-adaptation or chemical chaperones restore regular cell growth and division ('smooth' exponential growth).

Conclusions: Atypical, nonexponential growth at 44, 45 and 46 degrees C seems related to protein destabilization and can (partly) be restored by an appropriate medium design (i.e. addition of chemical chaperones) or temperature history (i.e. selection of a more resistant subpopulation).

Significance and impact of the study: This study indicates that the maximum temperature for growth is dependent on the temperature history and the chemical environment. These observations and the nonexponential kinetics have important implications for the development of predictive models for food safety and quality.