Pathogenicity of urinary tract infection Escherichia coli in Caenorhabditis elegans

Abstract

Uropathogenic Escherichia coli (UPEC) is a major bacterial pathogen that causes urinary tract infections (UTIs). Several virulence factors (VFs) in the bacteria have been associated with the pathogenicity. The mouse is an available UTI model for studying the pathogenicity; however, Caenorhabditis elegans represents as an alternative surrogate host for studying UPEC with the capacity for high-throughput analysis. Therefore, we established a simple assay for a UPEC infection model with C. elegans for large-scale screening. An E. coli culture to be tested and synchronized C. elegans were mixed in 96-well plates, and the pathogenicity was determined by comparison of the turbidity before and after incubation. A total of 133 clinically isolated E. coli strains, which included UTI-associated and fecal isolates, were applied to demonstrate the liquid pathogenicity assay. The E. coli isolates associated with UTIs showed higher pathogenicity in C. elegans than the fecal isolates, suggesting that the simple assay with C. elegans is useful as a UPEC infectious model. From the screening, VFs involved with iron acquisition (chuA, fyuA, and irp2) were significantly associated with high pathogenicity. C. elegans is a heme auxotroph, and iron homeostasis also serves innate immunity in C. elegans. We then evaluated whether the VFs in UPEC were involved in the pathogenicity. Mutants of E. coli UTI89 with defective iron acquisition systems were applied to a solid killing assay with C. elegans. As a result, the survival rate of C. elegans fed with the mutants significantly increased compared to when fed with the parent strain. To our knowledge, this is the first report of the involvement of iron acquisition in the pathogenicity of UPEC in a C. elegans model.