Summary: The pathogenic partially acid-fast lipophilic organism and a closely allied species were found capable of withstanding exposure to 90° for 10 min. when dispersed in phosphate buffer suspensions in small sealed ampoules. Denser suspensions withstood 3 min. at 100°. The nature of the medium on which the cells were grown did not seem to influence their thermoduric properties. Of the two morphotypes of that were originally isolated, one (G) consistently showed a higher degree of heat-resistance. The morphotypes were further distinguished by slight differences in the ‘feel’ of the cells and in their response to micromanipulative procedures. Different single cell isolates of the two morphotypes varied as regards thermotolerance, but the more resistant were G isolates. The lag period following heat treatment was generally accompanied by a compressed and stunted mode of growth, featuring prolonged angular division. Subsequent growth was normal.

Two strains of the pathogenic , as well as two saprophytic soil species of , were killed by exposures of 1-2 min. at 65°. An organism received as a blood culture and belonging to the group, was able to withstand 90° for 1 min. Subjection to heat treatment increased the inherent autolytic tendency of the culture and affected the type of sporophores produced during the first generation.


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