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Studies in the dynamics of disinfection. X. The effect of lethal temperatures on standard cultures of Bact. coli. III. on the variation of the rate of disinfection with temperature at pH 7·0, including the calculation of a new and constant temperature coefficient

Published online by Cambridge University Press:  15 May 2009

R. C. Jordan ,
S. E. Jacobs  and
H. E. F. Davies
R. C. Jordan
Affiliation:
From the Physiology Department, University College of South Wales and Monmouthshire, Cardiff, and the Bacteriological Laboratory, Imperial College of Science and Technology, London.
S. E. Jacobs
Affiliation:
From the Physiology Department, University College of South Wales and Monmouthshire, Cardiff, and the Bacteriological Laboratory, Imperial College of Science and Technology, London.
H. E. F. Davies
Affiliation:
From the Physiology Department, University College of South Wales and Monmouthshire, Cardiff, and the Bacteriological Laboratory, Imperial College of Science and Technology, London.
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1. The 99·99 % mortality time (t) has been used as a measure of the rate of disinfection of standard cultures of Bact. coli by heat under carefully controlled conditions, and the relationship between this rate and temperature (T) over the range 47–55° C. has been examined.

2. From the form of the relationship a minimum temperature of about 44° C. for the reaction was indicated, but the formula t (T — α)b = a, which has been used for the calculation of biological temperature coefficients in the past, was quite inadequate to express the relationship when an acceptable value for the maximum temperature (α) was employed.

3. The formula t × θT = A more usually employed in bacteriological work, fitted the data reasonably well except at the highest temperature. The very high value of 897 for Q10 was obtained.

4. On theoretical grounds, the above formula could not apply at temperatures near the minimum, and also it appeared likely to break down when high temperatures were used.

5. It was shown that the full graph of log (t — 10) against temperature should be sigmoid and asymptotic to two temperatures, a minimum and a maximum, the latter being defined as the temperature at which 99·99 % mortality would be produced in 10 min.

6. The graph of the Pearl-Verhulst logistic equation is of this type and, with 44 and 56° C. as the minimum and maximum temperatures, it provided an excellent fit to the data, especially at the highest temperature used.

Type
Research Article
Information
Journal of Hygiene , Volume 45 , Issue 3 , August 1947 , pp. 333 - 341
Copyright
Copyright © Cambridge University Press 1947

References

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