The Toxic Effect of Oxygen Upon the Aerosol Survival of Escherichia coli B

Abstract

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

The Aerosol Survival and Cause of Death of Escherichia coli K12

“…This effect, and that caused by RH changes before collection, indicated, as for the other three strains of E. coli studied, that the manner in which water enters the bacterium during collection influences the survival. Oxygen toxicity was less apparent with E. coli K I~ HfrC than, for example, E. coli B (Cox, 1966a;Cox & Baldwin, 1967)~ probably owing to the poor survival of the former in nitrogen at low RH (in the absence of protective agents). The action of glycerol and raffinose was very similar to that with E. coli JEPP (Cox, 1967)~ and again showed that at low RH a protective agent (namely rafiose) outside the cell wall was able to confer stability.…”

“…162). Of the four coli strains studied, E. coli ~1 2 HfrC was the most unstable at high and at low RH, and was a good organism with which to study death mechanisms other than oxygen toxicity (Cox & Baldwin, 1967), because of the extent of viability loss when sprayed from distilled water into a nitrogen atmosphere. The minimum at 85% RH was very similar to that found at the same RH for E. coli B, but was very apparent at a much shorter aerosol age.…”

“…aerosol age for Escherichia coli K12 HfrC sprayed from distilled water into air and into nitrogen. It is evident that air was slightly toxic, and by using mixtures of nitrogen and oxygen the lower survival in air was shown to be caused by oxygen, or a trace contaminant in it (see also Cox & Baldwin, 1967 …”

“…In particular, the aerosol survival of Escherichia coli has been found to depend upon several variables (Cox, 1965(Cox, , 1966a(Cox, , by 1967(Cox, , 1968Cox & Baldwin, 1964, 1966. These include an 'air stress' (Cox 1966a) at low relative humidity (RH), caused by the toxic action of oxygen, possibly modified by the presence of contaminants (Cox & Baldwin, 1967;Hess, 1965;Webb, 1967). At high RH, regions were found where E. coli survival was particularly sensitive to RH, in a manner dependent on the spray fluid and collecting fluid (Cox, 1966a(Cox, , b, 1967(Cox, , 1968Cox & Baldwin, 1966).…”

The Sensitivity of Gram-negative Bacteria, Recovered from Aerosols, to Lysozyme and Other Hydrolytic Enzymes

“…Bacterial survival in aerosols depends on a number of factors including relative humidity, composition of the gaseous environment and the compositions of both spray and collecting fluids (Webb, 1960;Cox, 1966a, b ;Benbough, 1967;Cox & Baldwin, 1967). Comparatively little is known about the effect of aerosolization upon the integrity of bacterial walls and membranes.…”