Effect of pH on Heat Inactivation of Bacteriophage. ∗

Abstract

It has been shown by Krueger 1 and confirmed by Dreyer and Campbell-Renton 2 that the heat inactivation of bacteriophage follows the course of a monomolecular reaction. In Krueger's data the increase in rate of inactivation with rise in temperature was very rapid (μ in the van't Hoff-Arrhenius equation = 101,000). Critical thermal increments of this order of magnitude are uniquely characteristic of protein denaturation and the experimental results with phage were consequently interpreted as indicating that inactivation involved denaturation as a significant factor. The present paper deals with the effect of pH on the heat inactivation of the same anti-Staphylococcus phage used in previous work.

2.5 ml. of standard anti-Staphylococcus phage containing 1 × 10¹⁰ activity units per ml. 3 was added to 2.5 ml. of beef infusion broth containing sufficient normal HCl to bring the final pH to the desired point. The samples were placed in a water bath adjusted to 57°C. for one-half hour and the residual (Phage) determined by the activity titration method. 3

Results are summarized in Table I and indicate that the phage suspension is most thermostable in the region of neutrality. At pH 7.0, 6.5, and 6.0 between 34% and 32% of the total original phage remains active; at pH 5.75 there is a sharp drop to 3% survival and at pH 5.5 to pH 4.0 less than 1% of activity is retained. On the alkaline side of neutrality the percentages of phage surviving the half-hour period of exposure to 57°C. are respectively: pH 7.5 = 50%) pH 8.0 = 24%, pH 8.5 = 10%, pH 9.0 and pH 9.5 less than 1%. With the exception of the data obtained at pH 5.5 and pH 9.5 the experimental results are regularly reproducible within narrow limits.