Survival of Escherichia coli from freeze–thaw damage: influence of nutritional status and growth rate

Abstract

The influence of nutritional status and growth rate on the cryosurvival of Escherichia coli was investigated. Organisms grown at rates between 0.1 and 0.6 h−1, under carbon- or nitrogen-limiting conditions all showed a basically similar cooling rate – survival profile; a peak of survival was noted in the lower cooling rate range (less than 100 C/min), a trough of minimum survival at 100 C/min, and increased survival as the cooling rate was increased to ultrarapid rates. Carbon-limited organisms showed a shift of the peak from 6 C/min for slowly grown organisms (D = 0.11) to 40 C/min at higher growth rates (D = 0.60 h−1); their survival at these peaks also showed a slightly upward trend. Nitrogen-limited organisms showed a similar trend of a shifting of the peak of survival. However, as the growth rate was increased, survival at this peak, and at other regions, decreased. For carbon-limited organisms, above 100 C/min, survival was growth rate independent, unlike nitrogen-limited organisms, which exhibited lower survivals as the cooling rate was increased in the ultrarapid range. The survival of both carbon-and nitrogen-limited organisms at the peak of survival showed a correlation with their carbohydrate and protein contents. The relevance of these findings is discussed.