Urinary tract infections (UTIs) will affect most women, can recur especially in postmenopausal women, and can become antibiotic recalcitrant. Escherichia coli causes most community-acquired UTIs and recurrent UTIs. Current theories of virulence, based on studies of UTI-associated E. coli , propose multiple virulence mechanisms and complex host-pathogen interactions.

Urinary tract infections (UTIs), mostly caused by uropathogenic E. coli (UPEC), are common bacterial infections that affect a majority of women and often recur. Genomic and transcriptomic analyses have not identified a common set of virulence genes which has suggested conserved virulence functions instead of virulence genes, multiple virulence mechanisms, and complex host-pathogen interactions. One aspect of the host-pathogen interaction is rapid UPEC growth in urine in vivo. When bacteria are grown in pooled urine, an averaged urine is assumed to diminish individual variation. We grew a non-pathogenic and pathogenic E. coli strains in urine from individuals who never had a UTI, had a UTI history but no current infection, and had a UTI history with a current infection. Bacterial growth showed large variations in individual urines and pooled urine supported significantly more growth than predicted for never and history groups but not the current group. UPEC strains, but not the non-pathogenic strain, were resistant to urinary inhibitory factors e.g., antimicrobial peptides based on an indirect inoculation-density effect assay. Total nutrient content tended to be higher in current group urine than never and history group urine. We propose that pooling optimizes a nutrient mixture in never and history group urines, which are often studied, whereas urine from current group individuals appear to have a more optimal nutrient mixture. We conclude that pooled urine is not "an average urine", and that the best comparisons of results between labs using pooled urine would also include results with a standardized synthetic urine.

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