Host Autophagy Diminishes Escherichia coli O157:H7 Epithelial Adhesion

Introduction: Escherichia coli O157:H7, is a leading Shiga Toxin-producing E. coli that has low infectious dose and causes serious illness in humans. E. coli O157:H7 gut colonization is the central problem leading to beef, dairy and green vegetable contamination, while adhesion to epithelial cells is the first step for E. coli O157:H7 to colonize, proliferation, and further develop infection and tissue damage in the gut. Autophagy is a pivotal catabolic process that has the ability to degrade unnecessary proteins and intracellular pathogens by activating autophagosomes.

Purpose: To study the impact of host autophagy and associated signaling on E. coli O157:H7 epithelial cell adhesion.

Methods: HT-29 cells were cultured in DMEM complete media, which were pre-treated with 10 ng/ml tumor necrosis factor (TNF)-α or subjected to starvation for 12 h. Then, cells were infected with E. coli O157:H7 for 4 h, and attached bacteria were serial diluted, plated and enumerated. Protein samples were further collected post E. coli O157:H7 infection for autophagy signaling analyses. 

Results: Both starvation and TNF-α pre-treatment enhanced autophagy in HT-29 cells as indicated by increased LC3B II/I ratio (P ≤ 0.05), which, on the other hand, decreased the adhesion of E. coli O157:H7 to HT-29 cells (P ≤ 0.01). Stress-activated protein kinases (SAPK)/Jun amino-terminal kinases (JNK) and endoplasmic reticulum stress sensor Inositol-requiring enzyme 1α (IRE1-α) regulate autophagy activation. Consistently, both of them were up-regulated by starvation but inhibited by E. coli O157:H7 infection. 

Significance:  Host autophagy plays a positive role in preventing E. coli O157:H7 from adherence to the host cells.