The Absence of Fimbriae Leads to Increased Intercellular Ag43-Ag43 Mediated Autoaggregation in Escherichia coli BW25113

Abstract

Type 1 fimbriae are filamentous polymeric structures found on the surface of Gram negative bacteria and drive non-specific adhesion to surfaces. In Escherichia coli, fimbriae are nearly ubiquitous and mediate host epithelial colonization during urinary tract infections. Similarly, the autotransporter antigen 43 (Ag43) mediates intercellular interactions and autoaggregation of E. coli cells, contributing to biofilm formation and bacterial persistence in host environments. Previous studies have suggested that pH modulation to decrease fimbriae expression may result in increased autoaggregation. In this study, we transformed wild-type and ∆fimA, ∆fimB, and ∆fimD knockout strains with plasmids encoding Ag43_(full), truncated Ag43_(∆193-551) or an empty vehicle (EV) control. Autoaggregation kinetics were assessed using an autoaggregation assay and western blots were done to evaluate protein expression in each transformed strain. Our results indicate that the absence of fimbriae in ∆fimA, ∆fimB, and ∆fimD KO strains leads to increased Ag43_(full)-mediated autoaggregation relative to the wild-type strain. The fimbriae likely physically obstruct intercellular Ag43-Ag43 interaction on neighbouring E. coli cells, limiting their physical proximity. Moreover, we observed that Ag43_(∆193-551) did not show increased autoaggregation and behaved more like the wild-type strain, suggesting that the C-terminal two-thirds of the Ag43 α subunit is necessary for intercellular interaction. Future studies should explore the rescue of fimbriae expression and confirm consistent fimbriae expression in the wild-type strains across different environmental conditions.