1989 Volume 44 Issue 3 Pages 756-762
Regarding airborne bacterial flora floating in outdoor air, Gregory1) has presented the following composition; 66% Micrococcus, 25% Bacillus, 6% Bacterium and 1 to 2% Vibrio. Wright et al.2) investigated the vertical distribution of airborne bacteria to 500 ft above the ground in the twin cities area and observed that bacterial flora at an altitude of 35 ft was composed of 28% Gram-positive asporogenic rods, 25% Gram-positive sporogenic rods, 17% Gram-positive cocci and Gram-negative rods and 14% diphtheroids. In the atmospheric layer ascending to 500 ft, the five groups of airborne bacteria decreased to about 1/3 to 1/5 of the amounts found at 35 ft. Mancinelli and Shulls3) investigated the airborne bacterial composition 10m above the ground in an urban environment where eleven genera of cocci, which were composed of 41% Micrococcus, 11% Staphylococcus and 8% Aerococcus, and seven genera of rods were recognized.
On the other hand, dynamic aspects of airborne bacteria have been also investigated with special reference to taxonomical and physiological characteristics of indicator strains. In 1946, Zo Bell4) reported that inland from a sea wall to a distance of 1600m, airborne bacteria occurring from the ocean could be estimated by a bacterial ratio developed on sea-water agar and fresh-water agar. Concerning the movement of bacteria by air current, Bovallius et al.5) investigated the migration of colored airborne particles together with a few adherent kinds of Bacillus in a sandstorm area from the Black Sea to Sweden. Recently, Fukaya et al.6) investigated the spread of airborne human enteric bacteria in an area around a sewage treatment plant established in the city of Nagoya. Distribution ratios of Enterobacteriaceae were 66% of the bacterial flora at the plant site and about 60% in the surrounding area. Taxonomical investigation of collected airborne bacteria revealed the presence of Enterobacteriacea such as Enterobacter agglomerans, Serratia rubidaea and Citrobacter freundii.
Our study was intended to elucidate some dynamic aspects of airborne bacterial flora over a wide area. Investigation was carried out by a filtration method using a soluble gelatin foam filter and continued for a year in an experimental area of the campus of the University of Occupational and Environmental Health (UOEH).
Airborne bacteria near the ground at station P were mainly composed of Gram-positive cocci and Gram-positive rods, but the bacterial compositions observed at each experiment that was repeated varied considerably in their ratios. The dispersion profile of bacterial flora over the experimental area, which was surveyed from observed results at stations A to E and P, indicated the existence of different floras corresponding to geographical features in areas around the observation stations. Airborne staphylococci collected at stations P and E were further investigated for the distribution of strains resistant to antibacterial reagents.
