A systematic comparison of four bioaerosol generators: Affect on culturability and cell membrane integrity when aerosolizing Escherichia coli bacteria

•Four bioaerosol generators were compared in terms of their physical and biological performance when aerosolizing E. coli bacteria.•Mechanical stress to bacteria during aerosolization resulted in the rupture of cell membrane and release of genomic DNA.•Damage to bacteria cell membrane was found to depend on generator type and aerosolization air pressure.•A newly-designed pneumatic nebulizer without liquid recirculation exerted less stress on test bacteria compared to the other three generators.

Bioaerosol research requires stable and reliable aerosol generators that can produce high particle concentrations with minimal damage to microorganisms. This study compared Collison nebulizer, Liquid Sparging Aerosolizer (LSA), C-Flow nebulizer, and a newly designed Single-Pass Aerosolizer with respect to their physical performance, and ability to preserve the culturability and structural integrity of bacteria. Escherichia coli bacteria were aerosolized at different air pressures, collected by a BioSampler and their Cell Membrane Damage Index (ID), expressed as the fraction of 16S rRNA gene copies in the supernatant liquid versus the amount of 16S rRNA gene copies in the total sample (cell pellet plus supernatant), was determined. The ID of E. coli aerosolized by the Collison and C-Flow nebulizers at 40 psi compared to aerosolization at 5 and 15 psi was significantly higher (p<0.05). However, the ID of E. coli aerosolized with the LSA and Single-Pass Aerosolizer did not seem to significantly depend on aerosolization pressure. The ID of E. coli collected with a BioSampler was found to positively and significantly correlate (p=0.043) with the presence of airborne bacterial fragments (aerodynamic size range 0.37–0.523 µm) as measured by the Aerodynamic Particle Sizer. Increased loss of culturability was observed for bacteria aerosolized by the Collison nebulizer and Single-Pass Aerosolizer with increasing aerosolization pressure (p<0.05), while no significant change in culturability was found for the other two generators as a function of aerosolization pressure. At particle output concentration of ~100 particles/cm3, the Single-Pass Aerosolizer preserved the culturability of bacteria significantly better than the other three generators (p<0.05). It also exhibited a significantly lower ID (p<0.001) and less culturability reduction (p=0.03) compared to the Collison nebulizer at particle output concentrations of ~1000 particles/cm3. It is hoped that this study will help bioaerosol researchers select a bioaerosol generator and method best suiting their studies.