Effect of Chilling on Bacteria in Aqueous Suspension

CEBTAIN bacteria in the logarithmic growth phase become non-viable when chilled in aqueous suspension. The phenomenon has been observed with strains of Escherichia coli1, Pseudomonas pyocyanea2 and Aerobacter aerogenes3. Loss of viability of logarithmic phase A. aerogenes suspended in chilled phosphate-saline is accompanied by the leakage of endogenous solutes, and the leakage products, in sufficient concentration, protect the bacteria against the lethal effect3. Thus, loss of viability is greater the sparser the population and is insignificant in chilled suspensions containing more than 5 × 109 organisms/ml. Correlation between loss of viability and leakage of endogenous solutes has now been obtained by observing the effects of chilling on three Gram-negative bacteria.