Abstract
This report presents in summary form the results of a study of the survival time of B. subtilis spores produced under a wide variety of nutritive and environmental conditions and exposed to high temperatures. The basic resistance has been defined as the resistance of a suspension of a definite density, produced and tested under certain standard conditions. The basic resistance of the strain employed was 6 minutes at 105° C, 14 minutes at 100° C, and 35 minutes at 95° C. Most of the determinations were made at 100° and 95°.
Pronounced deviations from the basic resistance have been produced by changing the nutritive substratum. The kind of peptone used has been found to be significant, but the resistance appears to have been independent of the concentration of the peptone.
Spores of diminished resistance were formed in all digest media tested with the exception of casein digest, which yielded spores of an enhanced resistance. The explanation of this probably rests on the difference in phosphate content of these media. Very resistant spores were formed in isoelectric gelatin. Evidence which has been acquired indicates that this was probably due to the low salt content of this medium. Infusions of vegetable matter were found to be excellent media. Spores of high resistance were formed in these media in all cases. Slightly more resistant spores were formed in liquid media than in solid media. Cultivation in the presence of a suitable concentration of either phosphate or magnesium resulted in the formation of spores considerably more resistant than the normal spores.
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