Murine Legionella pneumophilaInfection by Bioaerosol Inhalation in a Madison Aerosol Chamber Leads to Similar Disease Outcomes and Host Transcriptomic Responses as Intranasal Inoculation While Allowing for Bioaerosol Analysis

Legionnaire’s Disease is a growing concern for the United States and Europe, with disease incidences rising 6-fold since 2002. These recorded cases are increasingly associated with antibiotic resistant Legionella pneumophila, the causative agent of Legionnaire’s Disease and overall Legionellosis. With this, the need to study L. pneumophilainfections has never been greater. Current methodology for Legionella pneumophila infection studies often revolves around either artificial administration using intranasal or intratracheal delivery, semi-authentic delivery using bioaerosols and individual delivery systems (i.e. nose cones), or the burgeoning field of authentic exposure scenarios using aerosol generating showerhead devices. Here, we developed an alternative method using a Madison Aerosol Chamber as a means of generating and delivering bioaerosols in mice. We show that bioaerosol delivery using the Aerosol Exposure Chamber is very effective at exposing mice to various doses of L. pneumophila. RNASeq analyses revealed a robust immune response to bioaerosol delivered L. pneumophila comprising of activations of classical markers of infection and inflammation, including Cxcl and Ccl family genes and Il-1β. Similar gene expression profiles were observed when animals were intranasally exposed to L. pneumophila. Intranasal delivery resulted in a shorter duration of activation of several genes, indicating a lack of realistic infection response. Taken together, this evidence shows that our system delivers similar, if not better, results than intranasal inoculation while allowing researchers to study bioaerosol generation and delivery mechanisms simultaneously, critical factors for studying Legionella pneumophila infection. Such a new approach will allow for more accurate investigations to understand the effects of inhaling to Legionella contaminated drinking water. To understand immune response in murine lung tissue after either intransal or aersosol-based delivery of Legionella pneumophila we exposed two cohorts of mice to either treatment at comparable L. pneumophila dosages. Aerosol based delivery was performed in a Madison aerosol chamber. After exposure animals were sacrificed after 1hr, 24hr, 48hr, or 72hr with biological replicates included in each subset. Intransal instillation was delivered via a bolus of 5ul to each nostril followed by a 5ul PBS wash. After exposure animals were sacrificed after 1hr, 24hr, 48hr, or 72hr with biological replicates included in each subset. From each individual in each treatment lung tissue was immediately harvested for transcriptomic profiling. Additionally, for each treatment, control animals were included and handled/treated identically to their treated counter-parts, but without L. pneumophila exposure.