S U M M A R YAt high relative humidity (RH) similar survivals were obtained for storage in oxygen, air or nitrogen. At low RH the survival in nitrogen was much greater than that in air or in a 20 % (v/v) oxygen + 80 % (v/v) nitrogen mixture, in which the survivals were similar. In oxygen alone, survival was even lower than in air. Hence oxygen, or a trace contaminant in it, was responsible for the poorer survival in air than in nitrogen. The mechanism of death caused by oxygen is discussed. I N T R O D U C T I O NThe aerosol survival of Escherichia c d i has been shown by Cox (19664 b; 1967) to depend upon several variables. Amongst these was the nature of the atmosphere, in that at low relative humidity (RH), but not at high RH, survival was much greater in nitrogen than in air (Cox, 1966a;Cox & Baldwin, 1966). The previous suggestion that this survival difference was owing to the toxic action of oxygen (Cox, 1966a) is now examined. Hess (1965) found that at low RH, but not at high, oxygen caused enhanced death of aerosolized Serratia marcexens and Escherichia coli B. METHODSThe methods used were as previously reported (Cox, 1966a) except that in all experiments a rotating dnm container (Goldberg, Watkins, Boerk & Chatigny, 1958) was used for storing the aerosol cloud, and only Escherichia coli B sprayed from distilled water was studied. The drum apparatus used for the present work was similar to that used by Cox (1966a). Table I and show that at high RH similar survivals were obtained €or storage in oxygen (> 99*50/0), air or nitrogen (> 9909%). At low RH the survival in nitrogen was much greater than in air or in a 20 % (vlv) oxygen + 80 yo (vlv) nitrogen mixture, in which the survivals were similar. In oxygen alone survival was even lower than in air. Hence oxygen, or possibly a trace contaminant in it, was responsible for the poorer survival in air than in nitrogen. Analytical data of the oxygen did not suggest any obvious contaminants that were likely to have a toxic action at the parts per million concentrations at which they were present. However, such possibilities are not excluded completely since oxidizing agents such as ozone and the oxides of nitrogen at concentrations of a few parts per million might be toxic for Escherichia coli B in aerosols at low RH values. Also, oxygen+other 8-2 RESULTS Results are given in

SUMMARYThis paper presents data to show that loss of viability of Escherichia coli and phage in an aerosol was the consequence of at least three mechanisms.Phage T7 was used and shown to be unstable when sprayed into air. When previously adsorbed to E. coli the aerosol stability of phage T7 appeared to be dependent upon its stage of development in its host. The host E. coli strain B in an aerosol was itself subject to two stresses which operated through different mechanisms within the bacterium: (i) a relative humidity stress having its locus of action such that colony formation and the production of phage T7 were both impaired; (ii) an air stress such that colony formation was impaired but that the bacterium was able to produce phage T7.

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