Aerosol Survival of Pasteurella tularensis and the Influence of Relative Humidity

Abstract

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.

Survival and ice nucleation activity of bacteria as aerosols in a cloud simulation chamber

“…In experiments at constant temperature ranging from −18 • C to 49 • C, the survival rate of Mycoplasma pneumoniae, Serratia marcescens and Escherichia coli decreased with increasing temperature, while this had little or no effect on the survival of Bacillus subtilis (Ehrlich et al, 1970;Wright et al, 1969). The highest survival rates were invariably observed at extreme low and high levels of humidity (Cox and Goldberg, 1972;Wright et al, 1969). Finally, carbon monoxide concentration was shown to have variable impacts on the viability of airborne bacteria, with protective or deleterious effects depending on humidity and on the species (Lighthart, 1973).…”

“…Most studies aiming at predicting the death rate of airborne bacteria were carried out in the late 1960's and early 70's, with particular emphasis on the influence of temperature and relative humidity (Cox and Goldberg, 1972;Ehrlich et al, 1970;Lighthart, 1973;Wright et al, 1969). The ability of bacteria to survive as aerosols and the influence of abiotic parameters on survival were shown to strongly depend on the microorganism (Marthi et al, 1990).…”