Evaluation of Eight Bioaerosol Samplers Challenged with Aerosols of Free Bacteria (1992)

The need to quantify airborne microorganisms in the commercial microbiology industry (biotechnology) and during evaluations of indoor air quality, infectious disease outbreaks, and agriculture health investigations has shown there is a major technological void in bioaerosol sampling techniques to measure and identify viable and nonviable aerosols. As commercialization of microbiology increases and diversifies, it is increasingly necessary to assess occupational exposure to bioaerosols. Meaningful exposure estimates, by using area or environmental samplers, can only be ensured by the generation of data that are both precise and accurate. The Andersen six-stage viable (microbial) particle sizing sampler (6-STG) and the Ace Glass all-glass impinger-30 (AGI-30) have been suggested as the samplers of choice for the collection of viable microorganisms by the International Aerobiology Symposium and the American Conference of Governmental Industrial Hygienists. Some researchers consider these samplers inconvenient for evaluating industrial bioprocesses and indoor or outdoor environments. Alternative samplers for the collection of bioaerosols are available; however, limited information has been reported on their collection efficiencies. A study of the relative sampling efficiencies of eight bioaerosol samplers has been completed. Eight samplers were individually challenged with a bioaerosol, created with a Collison nebulizer, of either Bacillus subtilis or Escherichia coli. The samplers were evaluated under controlled conditions in a horizontal bioaerosol chamber. During each experimental run, simultaneous samples were collected with a reference AGI-30 to verify the concentration of microorganisms in the chamber from run to run and day to day. The results of this research indicate a wide variation in sample collection efficiency for free bacteria (i.e., mostly single cells of E. coli and B. subtilis, dac≥2µm). The particle concentration in the aerosol chamber, as indicated by the AGI-30 sampler, was 2000±85 colony-forming units per cubic meter (CFU/m3)for E. coli and 1170±400 CFUlm3 for B. subtilis. The collection efficiency of the evaluated AGI-30 relative to the reference AGI-30 was 101% + 4%. The 6-STG oversampled the reference AGI-30 by approximately 7%. However, the Andersen single-stage (1-STG), Mattson-Garvin Slit-to-Agar (STA), and Andersen two-stage (2-STG) samplers undersampled the reference AGI-30 by 7%, 10%, and 33%, respectively. The relative collection efficiencies of the Gelman 47-mm membrane filter (MF), Pool Bioanalysis Italiana surface air system (SAS), and Biotest Reuter centrifugal sampler (RCS) were <l%for E. coli. The low relative efficiency of the MF with E. coli was likely caused by desiccation of the organism. The SAS and RCS samplers, because of their design, are not efficient collectors of small particles. The relative efficiency of the MF with B. subtilis was 3% lower than that of the reference AGI-30 because this organism is an endospore-former and is more resistant to desiccation. For aerosols of free bacteria, the Andersen six-stage impactor, the Ace Glass AGI-30, and the Andersen single-stage impactor gave comparable results.