Growth conditions and heat resistance of Citrobacter freundii

The influence of the growth medium and the growth temperature on the heat resistance of Citrobacter freundii has been established. Logarithmic growth phase cells grown on rich media have a higher heat resistance than cells of the same phase grown on minimal media. This finding was independent of type of carbon source in the growth medium, but the kind of carbon source has a definite influence on the heat resistance. Logarithmic phase cells grown at 37 degrees C are much more heat stable than cells grown at 20 or 41 degrees C. Stationary growth phase cells are much more heat resistance than logarithmic phase cells, whereas Mg2+ - or glucose-starved cells are even slightly more heat stable than stationary phase cells.