Aug. 30, 1997 Current methods for detecting and counting airborne bacteria in enclosed buildings may be inadequate and understate the total number of airborne organisms, say researchers from the University of Maryland and the U.S. Environmental Protection Agency in the September 1997 issue of the journal Applied and Environmental Microbiology.
Indoor air pollution has become a serious concern. Newer, energy efficient buildings are usually sealed, recycling the air and increasing the number of bacteria in the environment. An estimated 10 to 25 million workers in the United States show symptoms of "sick building syndrome" (SBS) annually. The role of airborne bacteria in SBS is still largely unknown but it is generally accepted that microorganisms are involved.
In the study the researchers tested the effects of aerosolization on viability and colony-forming ability on several bacterial species. The bacteria were sprayed into glass containers and then total numbers were counted by two different methods. The first method was the method traditionally employed to determine indoor air quality where the the bacteria are cultured and the colonies formed are counted. The other was direct staining and counting of viable bacteria. The researchers found that less than 10 percent of the aerosolized bacteria were capable of forming colonies.
"From these results it is concluded that the bacterial strains included in this study did not respond to standard culture methods after aerosolization," say the researchers. "The plate [colony] count provides an estimate of only those few cells least affected by exposure to air." (J.F. Heidelberg, M. Shahamat, M. Levin, I. Rahman, G. Stelma, C. Grim, and R.R. Colwell. 1997. Effect of aerosolization on culturability and viability of gram-negative bacteria. Applied and Environmental Microbiology 63:3585-3588.)
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