Function and Regulation of Long Polar Fimbriae During Enterohemorrhagic Escherichia coli Infection

Walter J. Galdamez (Advisor: Anne-Marie Krachler, PhD)

Enterohemorrhagic Escherichia coli (EHEC) is a foodborne pathogen that causes severe gastrointestinal disease and hemolytic uremic syndrome. EHEC employs multiple virulence factors to colonize the host intestine, including the locus of enterocyte effacement (LEE) encoded type III secretion system, intimin, and flagella, yet the role of long polar fimbriae (Lpf) in adhesion and infection remains less well understood. Long polar fimbriae can mediate bacterial attachment to host cells in vitro, yet the regulation and function of its two fimbrial operons, lpf1 and lpf2, remain poorly understood. Preliminary RNA-seq data from zebrafish infected with EHEC reveal that expression of lpf1 and lpf2 is upregulated in regions of the midgut exposed to fluid shear stress, suggesting that mechanical cues may regulate expression during colonization. We hypothesize that long polar fimbriae subunits LpfA1, LpfA2, or both are essential for effective EHEC adherence and colonization of the intestinal tract and differentially expressed during infection. Here, we utilize a larval zebrafish (Danio rerio) model of foodborne EHEC infection to investigate their contribution to gut colonization. As a vehicle for foodborne infection, we use Paramecium caudatum, a unicellular protozoan and a natural prey of larval zebrafish. We demonstrate the major structural subunits of long polar fimbriae, LpfA1 and LpfA2, are required for efficient bacterial adherence and persistence within the zebrafish midgut. Deletion of lpfA1 and lpfA2 significantly reduced bacterial attachment, leading to lower EHEC recovery within the zebrafish midgut. Fluorescence imaging confirmed reduced gut colonization by lpf-deficient strains. Importantly, wild-type zebrafish that exhibit normal peristaltic movement generate intestinal shear forces that appear to enhance lpf expression and adherence, whereas sox-10^-/- deleted fish lacking coordinated peristalsis show reduced shear stress, correlating with altered bacterial colonization dynamics. These findings provide insight into EHEC pathogenesis and may inform future strategies to mitigate bacterial adhesion and infection.

Advisory Committee:

• Anne-Marie Krachler, PhD, Chair
• Souvik Bhattacharyya, PhD
• Anna Konovalova, PhD
• J. Christian Perez, PhD
• Diana Proctor, PhD