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...

Presently there is a significant effort to develop and evaluate vaccines and antibiotics against the potential bioterrorism agent Yersinia pestis. The animal models used to test these countermeasures involve the deposition of small particles within the lung. However, deliberate aerosol release of Y. pestis will generate both small and large inhalable particles. We report in this study that the pathogenesis patterns of plague infections caused by the deposition of 1-and 12-m-particle aerosols of Y. pestis in the lower and upper respiratory tracts (URTs) of mice are different. The median lethal dose for 12-m particles was 4.9-fold greater than that for 1-m particles. The 12-m-particle infection resulted in the degradation of the nasal mucosa and nasal-associated lymphoid tissue (NALT) plus cervical lymphadenopathy prior to bacteremic dissemination. Lung involvement was limited to secondary pneumonia. In contrast, the 1-m-particle infection resulted in primary pneumonia; in 40% of mice, the involvement of NALT and cervical lymphadenopathy were observed, indicating entry via both URT lymphoid tissues and lungs. Despite bacterial deposition in the gastrointestinal tract, the involvement of Peyer's patches was not observed in either infection. Although there were major differences in pathogenesis, the recombinant F1 and V antigen vaccine and ciprofloxacin protected against plague infections caused by small-and large-particle aerosols.In humans, Yersinia pestis infections present clinically as bubonic, septicemic, and pneumonic plague. The introduction of Y. pestis into the bloodstream by flea bites results in the characteristic lymphadenopathy of bubonic plague. Lymphatic and circulatory dissemination causes hematogenous seeding of the lungs, producing secondary pneumonia. Primary pneumonic plague arises from the inhalation of aerosols containing Y. pestis. Both bubonic and primary pneumonic plague can progress to septicemia, resulting in endotoxic shock during the terminal stages of infection (26,29). There is currently a high level of interest in biodefense models of airborne diseases for the identification of virulence mechanisms and the testing of medical countermeasures. The focus is on the pneumonic forms of these diseases caused by the inhalation of smallparticle aerosols.Over the past decade, and in the context of the possible use of Y. pestis in bioterrorism, there has been significant interest in devising therapeutics for pneumonic plague. Antibiotics including tetracyclines, streptomycin, and chloramphenicol are used to treat pneumonic plague (5, 44). Recently, the broadspectrum fluoroquinolone antibiotic ciprofloxacin has been proposed for postexposure prophylaxis for mass-casualty-setting plague (26). Ciprofloxacin possesses excellent pharmacokinetic properties, with high lung concentrations providing efficacy against murine pneumonic plague (11, 41, 42). Significant progress in the development of plague vaccines has been made. Vaccines containing F1 capsular polypeptide and LcrV (V) antigens protect agai...

Flow-focussing technology was harnessed to enable generation of large droplet aerosols within high-level microbiological containment. The Collison nebuliser and flow-focussing aerosol generator (FFAG) produced aerosols from distilled water with average mass median aerodynamic diameters (MMAD) of 4.19 and 11.93 lm, respectively. The medium type [water, phosphate buffered saline (PBS) or microbiological broth] had minimal effect on the droplet size generated by the FFAG. The FFAG can be modulated to generate reproducible aerosols with a wide range of MMADs (9-105 lm). The number of particulates (i.e. fluospheres) contained within the droplets increased as the MMAD increased from 12 to 50 lm. The technology described can be used for the exposure of small-animal models to large droplet aerosols ([10 lm) and has applications in healthcare, pharmaceutical, agricultural and biodefence environments.