Impact of dust exposure on mixed bacterial cultures and during eukaryotic cell co-culture infections

On a daily basis, humans, and their colonizing microbiome, are exposed to both indoor and outdoor dust, containing both deleterious organic and inorganic contaminants, through dermal contact, inhalation, and ingestion. Recent studies evaluating the dust exposure responses of opportunistic pathogens, such as Escherichia coli and Pseudomonas aeruginosa, revealed significant increases in biofilm formation following dust exposure. In this study, the effects of dust exposure on mixed bacterial cultures as well as HT-29 co-cultures were evaluated. As it was observed in pure, single bacterial cultures earlier, neither indoor nor outdoor dust exposure (at concentrations of 100 μg/mL) influenced the growth of mixed bacterial liquid cultures. However, when in paired mixed cultures, dust exposure increased sensitivity to oxidative stress and significantly enhanced biofilm formation (outdoor dust). More specifically, mixed cultures (E. coli-Klebsiella pneumoniae, K. pneumoniae-P. aeruginosa, and E. coli-P. aeruginosa) exhibited increased sensitivity to 20 and 50 mM of H₂O₂ in comparison to their pure, single bacterial culture counterparts and significantly enhanced biofilm production for each mixed culture. Finally, bacterial proliferation during a eukaryotic gut cell (HT29) co-culture was significantly more robust for both K. pneumoniae and P. aeruginosa when exposed to both house and road dust; however, E. coli only experienced significantly enhanced proliferation, in HT29 co-culture, when exposed to road dust. Taken together, our findings demonstrate that bacteria respond to dust exposure differently when in the presence of multiple bacterial species or when in the presence of human gut epithelial cells, than when grown in isolation.