Bacterial survival in evaporating deposited droplets on a teflon-coated surface

Understanding of bacterial survival in aerosols is crucial for controlling infection transmission via airborne aerosols and/or large droplets routes. The cell viability changes of four bacteria species (Escherichia coli K12 JM109; Acinetobacter sp. 5A5; Pseudomonas oleovorans X5; and Staphylococcus aureus X8), three Gram-negative and one Gram-positive, in a large evaporating droplet of size 1,800 microm in diameter on teflon-coated slides were measured using the LIVE/DEAD BacLight solution and a microscope. Droplets of three levels of salinity (0, 0.9, and 36% w/v) were tested. All four species survived well during the droplet evaporation process, but died mostly at the time when droplets were dried out at 40-45 min. The final bacteria survival rate after droplets were completely dried was dependent on bacteria species and the salinity of the suspension solution. Droplet evaporation over the first 35-40 min had no adverse effect on bacterial survival for the droplets tested. The lethal effect of desiccation was found to be the most important death mechanism.