Sterile Urine Notion Shown to Be a Myth

A new study has discredited the common belief that normal human urine is sterile.

Researchers at Loyola University (Chicago, IL, USA) evaluated urine specimens from 90 healthy women, collected directly from the bladder through aspiration or a catheter to avoid skin contamination. The specimens were analyzed using an expanded quantitative urine culture (EQUC) technique that can identify bacteria not detectable by standard urine culture techniques that are used to diagnose urinary tract syndromes. The study also used 16S rDNA sequencing to classify bacterial DNA.

The researchers found that bladder bacteria in healthy women differ from the bladder bacteria in those affected by an overactive bladder (OAB), and contribute to symptoms of urinary incontinence. The presence of bacteria could also correlate with other common lower urinary tract disorders, such as urinary tract infections and painful bladder syndromes. The results also revealed that some bacteria are more common in women with urgency urinary incontinence than in healthy women. The study was published in the March 2015 issue of European Urology.

“Clinicians previously equated the presence of bacteria in urine to infections. The discovery of bacteria in the urine of healthy females provides an opportunity to advance our understanding of bladder health and disease,” said lead author Prof. Alan Wolfe, PhD, of the department of microbiology and immunology. “Physicians and researchers must reassess their assumptions surrounding the cause of lower urinary tract disorders and consider new approaches to prevent and treat these debilitating health issues.”

It is commonly believed that urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultatively anaerobic Gram negative rods and cocci. Using EQUC, the researchers identified 35 different genera and 85 different species, with the most prevalent genera isolated being Lactobacillus (15%), followed by Corynebacterium (14.2%), Streptococcus (11.9%), Actinomyces (6.9%), and Staphylococcus (6.9%). Other genera isolated include Aerococcus, Gardnerella, Bifidobacterium, and Actinobaculum.

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