Substances which protect lyophilized Escherichia coli against the lethal effect of oxygen.

The lethal effect of oxygen on Escherichia coli organisms freeze-dried from water may be partly abolished by the addition of certain compounds before lyophilization. Three groups of such protective compounds were found: (i) thiourea, some of its derivatives and analogues; (ii) sugars, especially monosaccharides and some of their derivatives; (iii) some simple inorganic salts. The protective action was not unequivocally correlated with reducing power. Certain reducing agents (e.g. sodium dithionite, cysteine, reduced glutathione) even enhanced the lethal effects of oxygen.