(415c) Characterizing Population Motility and Growth of Pseudomonas Aeruginosa in Semisolid Gel Environments Using Bacterial Motility Assays.

Pseudomonas aeruginosa (PA) poses substantial health risks as nosocomial infections through their opportunistic colonization of vulnerable hosts and rapid acquisition of antibiotic resistance. PA is especially detrimental to long-term lung functionality among individuals with cystic fibrosis and chronic obstructive pulmonary disease where their impaired airway clearance helps harbor chronic respiratory infections. These multi-faceted metabolic and phenotypic adaptations are unique to the lung environment niche making representative in vitro models of PA pathogenic states crucial for identifying and assessing effective antimicrobial targets. Although in vitro platform designs have made considerable advancements mimicking the lung mucus microenvironment and microflora, a biophysical phenomenon omitted in these designs is bacterial motility through a gel interface. To better capture and represent the active PA propagation across lower respiratory tract airways through the lung mucus layer, we examine the applicability of the swim plate assay, an experimental platform for flagellar swimming motility, as an in vitro model for population-scale spatiotemporal evolution of pathogenic communities in semi-solid gel environments.

We adapted complementing timelapse microscopy and continuum mechanics modeling workflows to first measure the spatiotemporal distribution of isolate PA14 from an inoculation point and then contextualize the temporal PA14 motility and metabolic growth kinetics to separate model parameters [1]. We applied this workflow to different low density agar compositions incorporating methylcellulose or native MUC5AC lung mucin in order to characterize how the external gel environment affected PA14 spreading and growth. From collected microscope images, the continuum model determined that native MUC5AC lung mucin primarily had a confining effect on swimming motility when incorporated into the gel. This effect of MUC5AC extended beyond void fraction alterations as agar incorporating an equal weight fraction of methylcellulose did not alter PA14 motility. Interestingly, PA14 in swim plate assays yielded higher production of cytotoxic pyocyanin compared to PA14 in agitated liquid cultures, which further encourages application of the motility assay platform to establish dynamic, heterogeneous microbial communities.

[1] Cremer, J. et al. (2019). Chemotaxis as a navigation strategy to boost range expansion. Nature, 575. https://doi.org/10.1038/s41586-019-1733-y