The initial deviation from linearity of the thermal death rate curve of a putrefactive anaerobe.

Reynolds and Lichtenstein (Bact. Revs., 16, 126, 1952) have presented data that are inconsistent with the assumption that thermal death rate curves for spores of a putrefactive anaerobe (P.A. 3679) are exponential. Their data indicate that the survivor curve is sigmoid in nature, characteristic of populations made up of individuals of varying resistance. No evidence of clumping as a cause of initial deviation from linearity was obtained, and heat activation of suspensions ruled out any lag that would be attributable to the use of unactivated suspensions. In a further effort to determine whether the initial lag is real or an experimental artifact the following studies were carried out using the methods and techniques described by Reynolds and Lichtenstein with the exception that bicarbonate was used in the recovery medium and the incubation period was shortened to 7 days (Andersen, J. Bact., 62, 425, 1951; Reynolds, Kaplan, Spencer, and Lichtenstein, Food Research, 17, 153, 1952). The thermal death rate of a previously heat activated suspension of P.A. 3679 spores was determined in S0renson's phosphate buffer, M/15, pH 7, at 107 C on 3 separate runs with counts in triplicate for each time interval. Other aliquots of the original activated suspension were heated then at 107 C for 20 minutes. This period of time at 107 C was found in the previous death rate determinations to be just sufficient to bring the suspension to the point where the relationship between log number of survivors and heating time became approximately exponential. The heating was interrupted then by plunging the thermal death time tubes into ice water, and the thermal death rate of the 19531 245