# Loss of Type 1 Pili and Flagella in Uropathogenic Escherichia coli Leads to Reduced Phagocytosis by Human and Murine Monocytes

## TL;DR

Removing type 1 pili and flagella from UPEC bacteria reduces their chances of being eaten by immune cells, possibly helping them avoid detection in the body.

## Contribution

This study shows that removing type 1 pili and flagella in UPEC reduces phagocytosis by monocytes, suggesting a novel immune evasion strategy.

## Key findings

- A ΔfimA ΔfliC double mutant UPEC was phagocytized significantly less than the wild type strain.
- Loss of both type 1 pili and flagella reduces phagocytosis by human and murine monocytes.
- These structures may help UPEC evade innate immune defenses in certain environments.

## Abstract

Background: Uropathogenic Escherichia coli (UPEC) is the number one cause of urinary tract infections (UTIs) in humans. The ability to bind to uroepithelial cells through type 1 pili and ascend the urinary tract via flagella is important in the early stages of a UTI. However, both type 1 pili and flagella can also target the bacteria for elimination via monocytes/macrophages later in a UTI. We hypothesized that the loss of both type 1 pili and flagella on the UPEC cells would make them less likely to be phagocytized by phagocytic cells. Methods: In this study, ΔfimA, ΔfliC, and ΔfimA ΔfliC mutants were compared to the wild type UPEC strain NU149 in phagocytosis assays using human and murine monocytic cell lines. Results: A ΔfimA ΔfliC double mutant was phagocytized significantly less than the wild type strain. Conclusion: The data show that the loss of both type 1 pili and flagella expression on the UPEC cells reduces phagocytosis of the bacteria by human and murine monocytes. Although type 1 pili and flagella are important for establishing a UTI and ascension into the kidneys, the loss of these proteinaceous structures may allow the UPEC cells to evade the innate immune defenses in certain environments within the human body.