The Urinary Microbiota. Within internal surfaces, which are defined as existing outside the body (e.g. the intestinal epithelium or the vaginal epithelium), there exist commensal microbial communities. These microbiota are believed to be beneficial to human health, facilitating efficient removal of improperly functioning immune cells and protecting the host from pathogen infection13-15. The human bladder is a core component of the human urinary tract. It is a hollow muscular organ lined with transitional epithelium, which functions as the storage site for metabolic wastes in the form of urine. Given that the bladder's luminal space is also considered outside the body, it would seem reasonable that a urinary microbiota would be present. Yet, the historic dogma has maintained that urine is "sterile," based on culture-dependent methods of bacterial detection. This paradigm is shifting, however, based on our newly published data noting the presence of a urinary microbiota in adult women without clinical urinary tract infections16,17. Furthermore, we have recently discovered that the microbiota of women with overactive bladder (specifically with associated urgency incontinence) is distinguishable from the microbiota of women with stress urinary incontinence. These findings suggest that IC/PBS may be influenced by an alteration to the urinary microbiota. Indeed, recent evidence reports a difference in the urinary microbiome dominated by Lactobacillus in subjects with IC/PBS compared with healthy controls18. This work is limited by lack of correlative clinical symptomatology, small sample size and urinary samples that may have been contaminated.