AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Small Particle Aerosols of Francisella Tularensis; Characterization and Optimization to Support Pivotal Animal Efficacy Studies
Katherine O' Malley, Jennifer Bowling, Eileen Barry, Karsten Hazlett, DOUGLAS REED, University of Pittsburgh
Abstract Number: 181 Working Group: Bioaerosols
Abstract Evaluating vaccines and therapeutics for efficacy in animal models under the FDA’s Animal Rule requires development of a well-characterized and reproducible method for challenging animals. For bioterrorism threats like Francisella tularensis (Ft), aerosol dissemination is the likeliest means of a potential attack. We report here our efforts to characterize and optimize Ft aerosol performance, as well as improving precision and accuracy in dosing animals with Ft. A number of parameters were assessed for their impact on aerosolization of Ft including the choice of nebulizer, sampling device, exposure chamber, relative humidity, Ft strain selection and media used for propagation, aerosol generation/collection, and quantification. The Aeroneb, a vibrating mesh nebulizer which significantly improves aerosolization of influenza, was no better than the gold-standard 3-jet Collison nebulizer in aerosolizing Ft. Selection of impinger and flow rate through the impinger affected determination of aerosol concentration. Further complicating matters, flow cytometric analysis suggested that a large fraction of aerosolized Ft was in a ‘viable but not culturable’ state. Using Brain-Heart Infusion broth and keeping relative humidity >65% provided optimal Ft aerosol performance with little variability between individual aerosols on the same day or aerosols across a number of days. Improved accuracy in achieving desired nebulizer concentration greatly improved accuracy in achieving the desired target median inhaled dose, although precision in dosing between individual animals was not improved. Differences in individual animal minute volume during the 10-minute exposure largely account for the remaining variation. Choice of culture broth also affected outcome in vaccine studies; LVS-vaccinated rabbits survived challenge with lower morbidity and mortality if the virulent Ft for challenge was grown in MHB as opposed to BHI. This system is sufficiently robust and reproducible to meet the needs for pivotal efficacy studies but further characterization is warranted.