The deposition patterns of large-particle microbiological aerosols within the respiratory tract are not well characterized. A novel system (the flow-focusing aerosol generator [FFAG]) which enables the generation of large (>10-m) aerosol particles containing microorganisms under laboratory conditions was characterized to permit determination of deposition profiles within the murine respiratory tract. Unlike other systems for generating large aerosol particles, the FFAG is compatible with microbiological containment and the inhalational challenge of animals. By use of entrapped Escherichia coli cells, Bacillus atrophaeus spores, or FluoSphere beads, the properties of aerosols generated by the FFAG were compared with the properties of aerosols generated using the commonly available Collison nebulizer, which preferentially generates small (1-to 3-m) aerosol particles. More entrapped particulates (15.9-to 19.2-fold) were incorporated into 9-to 17-m particles generated by the FFAG than by the Collison nebulizer. The 1-to 3-m particles generated by the Collison nebulizer were more likely to contain a particulate than those generated by the FFAG. E. coli cells aerosolized using the FFAG survived better than those aerosolized using the Collison nebulizer. Aerosols generated by the Collison nebulizer and the FFAG preferentially deposited in the lungs and nasal passages of the murine respiratory tract, respectively. However, significant deposition of material also occurred in the gastrointestinal tract after inhalation of both the small (89.7%)-and large (61.5%)-particle aerosols. The aerosols generated by the Collison nebulizer and the FFAG differ with respect to mass distribution, distribution of the entrapped particulates, bacterial survival, and deposition within the murine respiratory tract.Environmental bioaerosols can have a profound influence on human health, due to infectious disease, hypersensitivity conditions (e.g., hay fever), and acute inflammatory responses resulting from the inhalation of irritants. Environmental aerosols comprise a polydisperse distribution composed of a range of particle sizes from submicron to large droplets thousands of microns in diameter. Hence, such aerosols contain a proportion of particles of Ͼ10 m, herein defined as "large particles." Indeed, analysis of the particle sizes containing bacteria within the atmosphere indicated that ϳ40% are greater than 7 m, due to adherence to debris (27). Environmental microbial aerosols can arise from a number of sources, including food processing (13,19,40); water sources, e.g., contaminated air conditioning systems, shower heads, water faucets, and cooling towers (2, 42, 53); pesticide sprayers (1); and fungal-spore generation (15, 26). The importance of bioaerosols from a civilian biodefense perspective was highlighted by the U.S. anthrax mail attacks in 2001 (3).In health care settings, nosocomial transmission may occur by patients coughing or sneezing, generating respirable particles within the diameter range of 0.5 to 12 m (6, 14); alternat...
