Intentionally disseminating spores such as Bacillus anthracis (anthrax) can cause much greater harm than their vegetative forms because of their extended survival in air. Characteristics of a bacterial cell, such as degree of hydration, growth medium (e.g., agar vs. broth), Gram stain (+ve vs. -ve), and metabolic state (vegetative vs. spore) affect its survival. Survival rates of different bacterial cells are also affected by exposure to different air environments. Temperature, relative humidity, ultraviolet light, and atmospheric pollutants are some factors that contribute to cell viability loss. These environmental factors minimally injure spores compared to both Gram-negative and Gram-positive vegetative cells. Neutralization of spore aerosol releases is critical in countering bioterrorism. As a possible spore aerosol neutralization method that avoids the use of chemicals, we investigate the mechanical instabilities of the bacterium cell envelope in air as bacteria are passed through aerodynamic shocks.
To carry out this fundamental investigation, an experimental impactor system is used to collect the spores after they pass through a controlled shock, and a detailed computational study is carried out to determine the impactor operating conditions that lead to bacterial break-up. Specifically, the bacteria experience relative deceleration because of sharp velocity changes in the aerodynamic shock created in the experimental impactor system. Computational model results indicate that B. atropheus spores require a critical acceleration of 3.9-16x109 m/s2 compared to 3.0x108m/s2 for vegetative E. coli to break-up consistent with our experimental findings. Our experimental results indicate that the fraction of cells surviving an aerodynamic shock with a maximum acceleration of 5.9x109 m/s2 is fl=0.030±0.010.
See more of this Group/Topical: Computing and Systems Technology Division