Quantitative sampling of indoor air biomass by signature lipid biomarker analysis

Exposure to airborne biocontaminants may result in a multitude of health effects and is related to a pronounced increase in adult-onset asthma. Established culture-based procedures for quantifying microbial biomass from airborne environments have severe limitations. Assay of the phospholipid fatty acid (PLFA) components of airborne microorganisms provides a quantitative method to define biomass, community composition and nutritional/physiological activity of the microbial community. By collecting airborne particulate matter from a high volume via filtration, we collected sufficient biomass for quantitative PLFA analysis. Comparing high (filtration)and low (impaction) volume air sampling techniques at 26 locations within the Eastern United States, we determined that PLFA analysis provided a viable alternative to the established but flawed culture-based techniques for measuring airborne microbial biomass and community composition. Compared to the PLFA analysis, the culture techniques underestimated the actual viable airborne biomass present by between one to three orders of magnitude. A case study of a manufacturing plant at which there had been complaints regarding the indoor air quality is presented. Phospholipid fatty acid characterization of the biomass enabled contamination point source determination. In comparison with samples taken outdoors, increases in the relative proportion of trans PLFA, reflecting shifts in the physiological status of viable airborne Gram-negative bacteria, were detected in the indoor air samples at a majority of sampling sites.