Evaluation of bioaerosol sampling techniques for Legionella pneumophila coupled with culture assay and quantitative PCR

Efficient bioaerosol sampling methods are required for characterization of exposure risk to airborne pathogenic Legionella pneumophila, which may cause severe pneumonia and death in humans. By using culture assay and quantitative PCR, the effects of sampler type, sampling time (1–60 min), collection fluid (deionized water (DW) and Tween mixture), and DW replenishment during sampling on the recovery of culturable and total L. pneumophila were assessed. Escherichia coli was also tested as a comparison. The collection efficiency was consistently greater for culturable L. pneumophila than E. coli by a factor of 2.7–12.2 (P=0.005). Besides, total and culturable bioaerosols were both recovered less in microbiological air sampler (MAS-100) by 1–2 orders of magnitude than in Andersen one-stage sampler (Andersen 1-STG), all-glass impinger (AGI-30), and BioSampler regardless of sampling time, bacterial species (L. pneumophila and E. coli), and collection principle (agar impaction and liquid impingement) (P<0.05). BioSampler was more efficient than AGI-30 to capture total L. pneumophila (P=0.003), whereas a comparable bioefficiency was found for culturable cells (P=0.74). DW obtained more culturable L. pneumophila than Tween mixture by a factor of 4.1–12.5 in BioSampler and 2.2–6.8 in AGI-30 during 3–60 min sampling (P<0.0001). Increasing sampling time deteriorated the accuracy of L. pneumophila quantification, particularly for culturable cells (P<0.0001). However, DW replenishment every 15 min during sampling significantly improved the recovery of culturable L. pneumophila in both AGI-30 and BioSampler by a factor of 3.3 and 7.1, respectively (P=0.001). Considering a longer sampling is preferred to quantifying airborne L. pneumophila usually at a low level of concentration, this study recommends to collecting this pathogen by BioSampler with periodical refilling of DW.