Nissle 1917 inhibits biofilm formation and mitigates virulence in .

In the quest for mitigators of bacterial virulence, cell-free supernatants (CFS) from 25 human commensal and associated bacteria were tested for activity against . Among these, Nissle 1917 CFS significantly inhibited biofilm formation and dispersed extant pseudomonas biofilms without inhibiting planktonic bacterial growth. eDNA was reduced in biofilms following exposure to Nissle CFS, as visualized by confocal microscopy. Nissle CFS also showed a significant protective effect in a -based larval virulence assay when administrated 24 h before challenge with the No inhibitory effects against were observed for other tested strains. According to proteomic analysis, Nissle CFS downregulated the expression of several proteins involved in motility (Flagellar secretion chaperone FliSB, B-type flagellin fliC, Type IV pilus assembly ATPase PilB), and quorum sensing (acyl-homoserine lactone synthase lasI and HTH-type quorum-sensing regulator rhlR), which are associated with biofilm formation. Physicochemical characterization of the putative antibiofilm compound(s) indicates the involvement of heat-labile proteinaceous factors of greater than 30 kDa molecular size.