Survival of Escherichia coli during drying and storage in the presence of compatible solutes

Five different compatible solutes, sucrose, trehalose, hydroxyectoine, ectoine, and glycine betaine, were investigated for their protective effect on Escherichia coli K12 and E. coli NISSLE 1917 during drying and subsequent storage. Two different drying techniques, freeze-drying and air-drying, were compared. The highest survival rate was observed when the non-reducing disaccharides sucrose (for E. coli K12) and trehalose (for E. coli NISSLE 1917) were added. The two tetrahydropyrimidines, hydroxyectoine and ectoine, gave protection to freeze-dried E. coli NISSLE 1917 whereas E. coli K12 was protected only by hydroxyectoine. Glycine betaine seemed to be harmful for both strains of E. coli with both drying techniques. Air-drying gave much better survival rates than freeze-drying. The two strains of E. coli differed in their ability to take up compatible solutes. (DBO)