Viable bacteriophage in CO2 laser plume: aerodynamic size distribution

The size of CO2 laser generated plume particles containing viable bacteriophage, phi X174, was determined with 2 models (10-830 and 15-500) of Andersen bioaerosol cascade impactors. Samples were collected during 100 one-second laser exposures (approximately 68 W/cm2) of a bacteriophage-agar substrate with and without a space-confining hood. The hood appeared to facilitate collection of the largest particles (P < 0.1). In addition, Andersen model 15-500 was a more efficient collector of the largest particles, a phenomenon which is likely a function of the dynamic nature of the laser plume as well as impactor design. We found that laser plume particles containing viable bacteriophage are very large, in one instance exhibiting a count median aerodynamic diameter (CMAD) and mass median aerodynamic diameter (MMAD) of 23 and 55 microns, respectively. Furthermore, the appearance of viable bacteriophage in these plume particles constitutes an extremely rare event. The limitations of cascade impactor design when used to analyze particles with high water concentrations generated in a laser plume are discussed.