Differential Effects of Uropathogenic and Non-Uropathogenic E. coli on the Mouse Urobiome and Urine NGAL Levels

To determine whether urine neutrophil gelatinase-associated lipocalin (uNGAL) or urobiome alterations can differentiate urinary tract infections (UTI) from asymptomatic bacteriuria (ASB).

Female 8-week-old C57BL/6 mice were instilled with either Escherichia coli CFT073 (UTI model, n=12), E. coli 83972 (ASB model, n=12), or saline (control, n=3). uNGAL was measured daily for 3 days post-instillation. Urobiome composition was assessed pre- and post-instillation using 16S rRNA sequencing. At day 3, kidneys were harvested for culture. Comparisons were made across groups for uNGAL levels and urobiome diversity.

Baseline β diversity did not differ between groups. Post-instillation, β diversity significantly differed across groups (p=0.01), driven by increased relative abundance of E. coli in UTI mice compared to ASB mice. Median uNGAL levels increased significantly in both UTI and ASB groups relative to controls, but no significant difference was observed between UTI and ASB groups.

Introduction of a uropathogenic E. coli strain reduced urobiome diversity, while a non-uropathogenic strain did not, suggesting strain-specific effects on microbial ecology. Bladder instillation itself also altered the urobiome. Elevated uNGAL levels were observed in both UTI and ASB models, indicating that while uNGAL reflects bacterial exposure, it does not distinguish between uropathogenic and non-uropathogenic E. coli. These findings highlight urobiome analysis as a potential tool for differentiating UTI from ASB, whereas uNGAL alone is insufficient.