(511w) A Study Of Bacterial Aerosol Neutralization By Shock Waves Using A Novel Impactor

Environmental bioaerosols can be categorized according to their source as natural or anthropogenic. Pollen, and bacteria associated with soil debris are examples of natural sources present at background concentrations. Anthropogenic bacterial aerosols can potentially be used as bioterrorism agents. Effective neutralization of the bioterrorism aerosol is necessary to minimize human casualties. Here, we investigate the use of shock waves to introduce mechanical stress, which results in death of the bacteria. This method avoids the use of chemicals that can be hazardous when used in the aerosol phase. We present a study of how bacteria interact with shock waves in compressible media (air). An aerosol impactor (the device consists of a converging nozzle through which the aerosol flows normal to an impaction surface) is designed capable of passing bacterial particles through a shock wave. The study presents insight into (1) the effectiveness of a shock wave in neutralizing bacterial aerosol and (2) the mechanisms causing loss of viability.

In a standard impactor the aerosol is collected on a plate at high velocity. The impaction has been shown to cause significant bacterial damage. The stopping distance of a 1μm bacterium entering stagnant air at 343 m/s (Mach 1) is ~1.0 mm. We designed a deceleration tube to ensure zero-velocity deposition after passing the shock.

The impactor allows variation of the shock strength and thickness by an adjustable nozzle to plate distance. The upstream and downstream nozzle pressures are operational parameters that can also change the shock strength and pressure.

Preliminary data using scanning electron microscopy (SEM) analysis indicate structural differences between intact bacteria (not subjected to the shock wave) and bacteria passed through the shock wave in the impactor. Structural differences are an important determinant in viability. Experiments using bio-assays on the sampled bacteria for a detailed characterization of their damage (percent dead or viable) are currently performed Our approach allows to simultaneously pass the bacteria through a shock and to collect the particles in the same system.. The simultaneous detection eliminates the need to sample the bacterial aerosol, compared with shock tube geometries thereby reducing sampling errors. An added advantage is that a modified version of this novel impactor, once tested can also serve as an environmental field sampler and detector.