The effect of cooling and warming rates on the survival of a variety of bacteria

Cooling and warming rates affect bacterial survival profoundly with all bacteria tested (Azotobacter chroococcum, Klebsiella aerogenes, Salmonella typhimurium, Pseudomonas aeruginosa, Streptococcus faecalis) behaving similarly. Most bacteria were sensitive to salt on freezing and thawing. Viabilities of population frozen and thawed in saline were always less (by at least 20%) than comparable ones frozen in water alone. Under these conditions, S. faecalis was resistant to the presence of sodium chloride; viabilities of populations frozen in the presence or absence of sodium chloride were always less than 5% different. The implications of these results in light of the organisms' shape, Gram stain, and respiration are discussed.