A QUANTITATIVE STUDY OF THE DEPOSITION AND CLEARANCE OF BACTERIA IN THE MURINE LUNG.

Recent bacteriologic studies have shown that the bronchial secretions of human beings are usually sterile in the absence of evident broncho-pulmonary disease (1-3). However, bacterial contamination of the bronchi by inspired air, and perhaps by upper respiratory tract secretions, can be considered to be a common occurrence. For example, when radiopaque media are instilled into the pharynges of sleeping individuals, radi-opacity can often be detected in the lungs after-ward (4). Thus, the absence of bacteria in the bronchi suggests that potent antibacterial mechanisms are continuously operative (3). The capacity of bronchopulmonary tissue to dispose of foreign materials, including bacteria, has been recognized for many years. Stillman (5) and Hamburger and Robertson (6) observed that pneumococci disappeared from the peripheral portions of the lungs of mice and dogs within a few hours after sprays of pneumococci had been instilled. On the other hand, oropharyngeal com-mensals and potential respiratory pathogens can be isolated from the bronchial secretions of patients with chronic bronchitis during relatively quiescent periods in their disease, i.e., in the absence of increased symptomatology and signs of infection (3). The bacteria that are found in such secretions are usually present in numbers exceeding 106 colonies per milliliter of secretions (3). Such a finding implies impairment of the antibacterial mechanisms of the respiratory tract in chronic bronchitis and indicates the need for further study of the mechanisms by which the * bronchopulmonary system retains its sterility. Presumably, insight into such mechanisms would provide a basis for understanding better the pathogenesis of chronic bronchopulmonary infection. The present study was designed to investigate the quantitative implantation and clearance of aerosolized bacteria in the lungs of small animals. Many early experiments with airborne contagion employed coarse sprays and systems that were difficult to quantitate. Precise aerosol-exposure systems were introduced by Wells, who demonstrated that droplet nuclei play a key role in the aerial transmission of disease (7, 8). Bacteria in minute-dried residues of evaporated droplets live suspended in air for hours, and in this state they are inhaled and deposited in pulmonary tissue ., Aerosol devices were further developed in large-scale cloud chamber studies (9). Lurie, Heppleston, Abramson, and Swartz (10) and Middlebrook (11) also adapted these techniques to the experimental production of pulmonary tuberculosis. Most of the experimental equipment for such studies is complex and costly. This report describes an inexpensive, compact aerosol exposure system that offers a relatively simple method for the …