GERALi) T. CARGO, ANI) ROBERT R. ERNST. Kinetics of heat activation and of thermal death of bacterial spores. Appl.-Microbiol. 11:485-487. 1963. Hypotheses concerning kinetics of heat activation and of thermal death of bacterial spores were formulated, and were employed to derive equations describing nonlogarithmic thermal death curves. The equations permitted evaluationi of the validity of experimental data and provided a means for testing the hypotheses presented.

SHULL, JAMES J. (Wilmot Castle Co., Rochester, N. Y.) AND ROBERT R. ERNST. Graphical procedure for comparing thermal death of Bacillus stearothermophilus spores in saturated and superheated steam. Appl. Microbiol. 10:452-457. 1962-The thermal death curve of dried spores of Bacillus stearothermophilus in saturated steam was characterized by three phases: (i) a sharp initial rise in viable count; (ii) a low rate of death which gradually increased; and (iii) logarithmic death at maximal rate. The first phase was a reflection of inadequate heat activation of the spore population. The second and third phases represented the characteristic thermal death curve of the spores in saturated steam. A jacketed steam sterilizer, equipped with a system for initial evacuation of the chamber, was examined for superheat during normal operation. MNeasurements of spore inactivation and temperature revealed superheat in surface layers of fabrics being processed in steam at 121 C. The high temperature of the fabric surfaces was attributed to absorption of excess heat energy from superheated steam. The superheated steam was produced at the beginning of the normal sterilizing cycle by transfer of heat from the steam-heated jacket to saturated steam entering the vessel.

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Hypotheses concerning kinetics of heat activation and of thermal death of bacterial spores were formulated, and were employed to derive equations describing nonlogarithmic thermal death curves. The equations permitted evaluation of the validity of experimental data and provided a means for testing the hypotheses presented.

The relationships of reaction temperature and concentration of gaseous ethylene oxide to the time required for inactivation of air-dried Bacillus subtilis var. niger spores are more complex than previously reported. A plot of temperature vs. the logarithm of “thermochemical death time” (TCDT) resulted in a straight line between 18 and 57 C for systems of “high” ethylene oxide concentration. The TCDT values were independent of ethylene oxide concentrations above certain temperature-dependent limits. A given ethylene oxide concentration produced a TCDT curve identical in the upper temperature regions with that for higher concentrations. As the temperature was lowered beyond a critical point, this curve diverged from that for higher concentrations, as a straight line of lesser slope. Thus, a series of curves exists for a range of ethylene oxide concentrations. They are characterized by two segments, both logarithmic, intersecting at a critical temperature for each concentration. The intersecting point is at a temperature inversely related to the ethylene oxide gas concentration. The temperature quotient for the high temperature segments of all systems was 1.8. This value was characteristic for ethylene oxide concentrations of 440 and 880 mg/liter at temperatures above 40.6 and 33.4 C, respectively. Below these critical temperatures, the Q 10 values for the respective systems were 3.2 and 2.3.