Studies on Thermophilic Bacteria

Abstract

1. Eighty-nine strains of bacteria, studied according to the index number as expressed on the descriptive chart of the Society of American Bacteriologists, fell into twelve classes. All of these separations are based upon unessential characteristics of classification. In the light of this fact, the thermophilic group seems to be a homogeneous one, the members having in common all of the important characteristics used in classification. 2. A tentative separation of bacteria into groups on the basis of reaction to temperature has been presented. 3. The ability to grow at high temperatures seems to be a somewhat relative function, depending on the conditions of incubation. The so-called strict thermophilic bacteria, however, show a much more rapid growth at 55°C. than at lower temperatures. They must be distinguished from thermo-tolerant bacteria. 4. The thermal resistance of eighteen strains of thermophilic bacteria was studied. At the higher temperatures, 115°C and 120°C., the thermal death points fell within narrower time limits than those at the lower temperatures, 100°, 105°, and 110°C. 5. The "index number" is a distinct improvement upon the old "group number," although some of the points in the "index number" would be difficult to determine. For instance, the function of pathogenicity could not be determined without a great deal of experimental work. 6. The character of the media influenced the temperatures for the growth of thermophiles.