Aims: Non-sigmoid growth curves of Escherichia coli obtained at constant temperatures near the maximum growth temperature (T(max)) were previously explained by the coexistence of two subpopulations, i.e. a stress-sensitive and a stress-resistant subpopulation. Mathematical simulations with a heterogeneous model support this hypothesis for static experiments at 45 degrees C. In this article, the behaviour of E. coli, when subjected to a linearly increasing temperature crossing T(max), is studied.
Methods and results: Subpopulation dynamics are studied by culturing E. coli K12 MG1655 in brain heart infusion broth in a bioreactor. The slowly increasing temperature (degrees C h(-1)) starting from 42 degrees C results in growth up to 60 degrees C, a temperature significantly higher than the known T(max). Given some additional presumptions, mathematical simulations with the heterogeneous model can describe the dynamic experiments rather well.
Conclusions: This study further confirms the existence of a stress-resistant subpopulation and reveals the unexpected growth of E. coli at temperatures significantly higher than T(max).
Significance and impact of the study: The growth of the small stress-resistant subpopulation at unexpectedly high temperatures asks for a revision of currently applied models in food safety and food quality strategies.