Survival of microorganisms after ultrarapid freezing and thawing.

Numerous reports during the past 75 years have described, usually in qualitative terms, the survival of various bacteria, yeasts, and fungi after exposure to very low temperatures (Smith, Biological Effects of Freezing and Supercooling, p. 74-137, The Williams & Wilkins Co., Baltimore, 1961). Although rates of cooling and warming have been shown to affect survival quantitatively (Mazur, Ann. N.Y. Acad. Sci. 85:610-629, 1960), the effects of extremely rapid rates (hundreds of degrees per second) have been reported a 26-gauge hypodermic needle onto a moving surface of sterile liquid nitrogen. Frozen droplets were collected and thawed by sifting slowly into stirred 0.15 M aqueous sodium chloride at 37 C. Cooling and warming rates of several hundred degrees per second have been calculated for these conditions (Rinfret, Ann. N.Y. Acad. Sci. 85:576, 1960). Viable-cell counts were made before freezing and after thawing from known dilutions by plating on Difco nutrient agar or Difco Sabouraud Dextrose Agar.