Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2017

Presence of Bacillus licheniformis in geogenic dust may enhance the susceptibility of respiratory epithelium to NTHi infection (#169)

Janessa L Pickering 1 , Teck Hui Teo 1 , Holly Clifford 1 , Ruth Thornton 2 , Lea-Ann Kirkham 2 , Graeme Zosky 3
  1. Telethon Kids Institute, University Of Western Australia, Subiaco, WA, Australia
  2. School of Paediatrics and Child Health, University of Western Australia, Perth, WA, Australia
  3. School of Medicine, University of Tasmania, Hobart, Tasmania, Australia

The development and progression of chronic lung diseases such as bronchiectasis involve recurrent episodes of severe bacterial respiratory infections. Contemporary studies indicate environmental dust exposure leads to more common and severe bacterial infections in the human airway. We have shown that exposure of human airway epithelial cells (AEC) to community-sampled dust particulate matter <10µm diameter (PM10) from remote Western Australia, significantly increased the ability of Non-typeable Haemophilus influenzae (NTHi) to attach and invade cells. Persistent microbial contamination within dust cultures prompted 16S rRNA sequencing and identification of Bacillus licheniformis, a spore-forming and environmentally abundant bacteria. Heat treatment (100°C) of all PM10 samples reduced their inflammatory properties suggesting heat-labile and/or microbial factors are essential for the effect of dust on respiratory epithelia. We therefore investigated the potential of the environmental B. licheniformis strain we isolated to induce AEC inflammation and exacerbate NTHi infection.

Immortalized human AEC (NuLi-1) were exposed to increasing doses of B. licheniformis (MOI 0.01, 0.1 and 1:1 bacteria:cells) for 1, 3, or 24 h. Trypan blue staining was used to determine epithelial cell viability. A co-colonisation challenge with both B. licheniformis and NTHi was assessed using a standard gentamicin survival assay. Epithelial release of IL-6 and IL-8 was determined using a bead based immunoassay.

B. licheniformis was cytotoxic to NuLi-1 at 24 h, likely due to its production of an extracellular protease. Compared with NTHi, B. licheniformis evoked significantly greater IL-6 and IL-8 inflammatory responses (p<0.0001 and p<0.0001 respectively). Simultaneous co-colonisation of B. licheniformis with NTHi did not increase NTHi infection, suggesting pre-colonisation with B. licheniformis is required for exacerbation.

These findings have important implications for the lung health of individuals living in arid environments, who are exposed to high levels of geogenic dust. Further investigation into the contribution of B. licheniformis and the wider dust microbiome to respiratory infection is warranted