Biofilm formation by Histophilus somni on 3D bovine respiratory tissue cultures.

The development of bacterial biofilms following infection involves bacterial attachment to tissues and maturation of the biofilm matrix (BM). However, studying the development of bacterial biofilms in vivo is difficult to follow. An established example of biofilm formation during host infection is bovine respiratory disease (BRD) due to Histophilus somni. To more accurately investigate in vivo biofilm development, three-dimensional bovine airway organoids comprised of bovine turbinate epithelial (BE) and pulmonary artery endothelial (BAE) cells embedded in type I collagen were developed. Cell-free concentrated culture supernatant (CCS) from biofilm-grown H. somni suppressed proliferation of epithelial cells more than endothelial cells, affected epithelial barrier integrity by disrupting ZO-1 localization, and induced robust IL-6 secretion in epithelial cells. The organoids were inoculated with H. somni to establish biofilms, which were examined by confocal laser-scanning microscopy of fluorescein-conjugated Moringa M lectin (specific for the exopolysaccharide of H. somni BM). Biofilm development progressed from attachment at day 3 to extracellular matrix elaboration enveloping BE and BAE by day 5. This organoid recapitulates key features of H. somni pathogenesis, such as barrier disruption, inflammatory signaling, and mature biofilm formation in relevant tissues. Thus, organoids provide a biologically relevant platform for mechanistic BRD studies and for evaluating vaccines or antimicrobials targeting biofilm-associated disease.