FACTORS INFLUENCING THE SURVIVAL OF SPIROCHETES IN THE FROZEN STATE.
TITRATION EXPERIMENTS MADE WITH RELAPSING FEVER SPIROCHETES BEFORE AND AFTER FREEZING SHOWED THE FOLLOWING: 1. With each freezing and thawing there is a slight but regular decrease in virulence, which decrease bears no relation to the duration of storage at - 78 degrees C. Ordinarily infectivity is destroyed by more than 4 refreezings. 2. There was not always close correlation between motility and infectivity. 3. Cooling spirochetes from 0 degrees C. to -78 degrees C. over a 2 to 6 hour period damages them only slightly more than does rapid cooling, but warming from - 78 degrees C. to 0 degrees C. over a 2 to 6 hour period kills most of the organisms. Rapid thawing, as in a water bath, damages the spirochetes less than thawing more slowly, as at room temperature. 4. At storage temperatures of -12 degrees C. and -20 degrees C. there is a gradual decrease in virulence over a period of days or weeks, and by the 6th week the infectivity of the material is markedly reduced.
Department of Bacteriology of The Johns Hopkins School of Hygiene and Public Health, Baltimore.
T B
TB
Turner
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Brayton