Survey of Culturable Airborne Bacteria at Four Diverse Locations in Oregon: Urban, Rural, Forest, and Coastal

Abstract

To determine the risks of microbial air pollution from microorganisms used for pesticides and bioremediation, or emanating from composting, fermentation tanks, or other agricultural and urban sources, airborne microbial levels must be evaluated. This study surveyed the atmospheric load of culturable bacteria at four locations in Oregon: a city street, a rye grass field, a Douglas fir forest, and a bluff on the Pacific coast. Samples (20–60 min each) were taken using slit and six-stage cascade samplers. Samples were taken over two 10- or 24-h periods, depending on the site. Meteorological measurements were made at each location. The quantity and type of bacteria found varied by location and time. The highest average number of bacteria during daylight hours was exhibited at the urban site (609 cfu/m3), followed by the forest site (522 cfu/m3), then the rural site (242 cfu/m3), with the lowest concentration found at the coastal site (103 cfu/m3). During the 24-h sampling periods at the rural site, bacterial concentration, in general, tended to increase at sunrise, decrease during the solar noon hours, gradually increase until sunset, then decrease into the evening, with the lowest concentrations occurring between 2100 and 0500 hours. Pigmented bacteria represented between 21 and 62% of the total bacteria sampled; the highest percentage of pigmented bacteria was found at the rural site, and the lowest percentage at the forest site. Bacillus was found to be the most abundant single genus represented at all locations (12–45%). The majority of bacteria found were associated with particles greater than 3 μm aerodynamic diameter. Information gathered from this survey combined with data from the literature and future surveys will contribute to the detection and description of microbial air pollution.