Methods For Counting Airborne Bacteria Inadequate, Say Researchers

     Indoor air pollution has become a serious concern.  Newer, energyefficient buildings are usually sealed, recycling the air and increasing thenumber of bacteria in the environment.  An estimated 10 to 25 millionworkers in the United States show symptoms of "sick buildingsyndrome" (SBS) annually.  The role of airborne bacteria in SBS is stilllargely unknown but it is generally accepted that microorganisms areinvolved.

     In the study the researchers tested the effects of aerosolization onviability and colony-forming ability on several bacterial species.  Thebacteria were sprayed into glass containers and then total numbers werecounted by two different methods.  The first method was the methodtraditionally employed to determine indoor air quality where the thebacteria are cultured and the colonies formed are counted.  The other wasdirect staining and counting of viable bacteria.   The researchers foundthat less than 10 percent of the aerosolized bacteria were capable offorming colonies.

     "From these results it is concluded that the bacterial strains includedin this study did not respond to standard culture methods afteraerosolization," say the researchers.  "The plate [colony] count providesan 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 onculturability and viability of gram-negative bacteria.  Applied andEnvironmental Microbiology 63:3585-3588.)