The aerosol survival in air was determined for Pasteurella tularensis live vaccine strain (LVS) as a function of relative humidity (RH). Three different preparations of bacteria were used: (i) liquid suspension of P. tularensis LVS in spent culture medium; (ii) powders of P. tularensis LVS freeze-dried in spent culture fluid; (iii) P. tularensis LVS freeze-dried in spent culture fluid and then reconstituted with distilled water and disseminated as a liquid suspension. Preparation (i) gave greatest survival at high RH and lowest survival at intermediate RH. Preparation (ii), in contrast, gave greatest survival at low RH and minimum survival at 81% RH. Preparation (iii) was the same as preparation (i), i.e., the process of freeze-drying and reconstituting with distilled water before aerosol formation had little or no effect upon aerosol survival as a function of RH. Hence, control of aerosol survival appears to be through the water content of P. tularensis LVS at the moment of aerosol generation rather than the water content of the bacteria in the aerosol phase.

Aerosols↗

PubMed1971

Effects of oxygen on aerosol survival of radiation sensitive and resistant strains of Escherichia coli B.

The aerosol survivals in air and nitrogen of radiation sensitive and resistant mutants of Escherichia coli B have been determined with logarithmic and resting phase bacteria. No consistent correlation was found between radiation sensitivity and aerosol sensitivity in the strains tested. Hence, the phenotypes Fil Hcr Exr, which determine sensitivity to radiation, do not influence aerosol survival, i.e. these known mechanisms which repair radiation-induced damage do not operate in aerosol stressed E. coli. In all cases the survival in air was less than that in nitrogen particularly so for E. coli B(s-1). The effect is explained in terms of a toxic action of oxygen. Comparison of survival of log and resting phase bacteria show that log phase cells are less aerosol stable than are resting phase cells. The ability to synthesize DNA in bacteria collected from the aerosol was less than in control unstressed bacteria, and this effect was independent of the presence of oxygen. Reduced ability to synthesize DNA could have been caused by reduced metabolic activity. It is shown that two different death mechanisms occur simultaneously in aerosols at low relative humidity. One mechanism is oxygen dependent and the other oxygen independent. The former was not through a decrease in metabolic activity, whereas the latter could be.

Aerosols↗

PubMed1971

Aerosol survival of Pasteurella tularensis disseminated from the wet and dry states.

The aerosol survival in air and in nitrogen was measured for Pasteurella tularensis live vaccine strain, disseminated from the wet and dry states. The results showed that most of the loss of viability occurred in less than 2 min of aerosol age, i.e., a rapid initial decay followed by a much slower secondary decay. In nitrogen and air, minimum survival occurred at 50 to 55% relative humidity (RH) for wet dissemination and at 75% RH for dry dissemination. This shift indicated that aerosols produced by wet and dry dissemination were not equivalent and suggested that survival might not be related to bacterial water activity or content. The results showed that rehydration is the key process with regard to survival, but that lysis on rehydration is not a primary death mechanism. The effects of oxygen were complex because it could be either protective or toxic, depending upon other conditions. The protective action of oxygen was through an effect on the spent culture suspending fluid. The latter contained a toxic component, the activity of which is suppressed by oxygen; possibly the component is pumped away during freeze-drying. A toxic effect of oxygen was not found in the presence of spent culture media because the toxicity of the latter masks such an effect. With other bacterial suspending fluids, oxygen was shown to be toxic at low RH. Similar effects with regard to oxygen toxicity were also found with a laboratory strain of P. tularensis. Differences in oxygen toxicity for aerosols generated from the wet and dry states also suggest that bacterial water content and activity do not control aerosol survival.

Aerosols↗

PubMed1970

Aerosol survival of Escherichia coli B disseminated from the dry state.

Survival was determined for Escherichia coli B disseminated as an aerosol from the dry state. Survival in nitrogen, like that for wet dissemination, was better at low than at high relative humidity (RH). At high RH, survival was characterized by critical zones of instability in survival as a function of RH, instability occurring at 100, 95, 78, 70, and 60% RH. In air, survival was inferior to that in nitrogen at low RH, whereas the converse was found at high RH. The effect was attributed to oxygen. In general, results support the conclusion that to the first approximation survival is related to bacterial water content, the latter increasing with RH. However, a more detailed analysis of results indicates that survival might not be exactly related to bacterial water content. It is shown that death occurred because of rehydration and that the pretreatment of E. coli B affected its aerosol stability characteristics; i.e., wet and dry disseminated aerosols are not equivalent.

Aerosols↗

PubMed1970

Experimental technique for studying aerosols of lyophilized bacteria.

An experimental technique is presented for studying aerosols generated from lyophilized bacteria by using Escherichia coli B, Bacillus subtilis var. niger, Enterobacter aerogenes, and Pasteurella tularensis. An aerosol generator capable of creating fine particle aerosols of small quantities (10 mg) of lyophilized powder under controlled conditions of exposure to the atmosphere is described. The physical properties of the aerosols are investigated as to the distribution of number of aerosol particles with particle size as well as to the distribution of number of bacteria with particle size. Biologically unstable vegetative cells were quantitated physically by using (14)C and Europium chelate stain as tracers, whereas the stable heat-shocked B. subtilis spores were assayed biologically. The physical persistence of the lyophilized B. subtilis aerosol is investigated as a function of size of spore-containing particles. The experimental result that physical persistence of the aerosol in a closed aerosol chamber increases as particle size is decreased is satisfactorily explained on the bases of electrostatic, gravitational, inertial, and diffusion forces operating to remove particles from the particular aerosol system. The net effect of these various forces is to provide, after a short time interval in the system (about 2 min), an aerosol of fine particles with enhanced physical stability. The dependence of physical stability of the aerosol on the species of organism and the nature of the suspending medium for lyophilization is indicated. Also, limitations and general applicability of both the technique and results are discussed.

Aerosols↗

PubMed1969