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.