Research Article: Detection of Intracellular Bacterial Communities in Human Urinary Tract Infection

Date Published: December 18, 2007

Publisher: Public Library of Science

Author(s): David A Rosen, Thomas M Hooton, Walter E Stamm, Peter A Humphrey, Scott J Hultgren, Steven M Opal

Abstract: BackgroundUrinary tract infections (UTIs) are one of the most common bacterial infections and are predominantly caused by uropathogenic Escherichia coli (UPEC). While UTIs are typically considered extracellular infections, it has been recently demonstrated that UPEC bind to, invade, and replicate within the murine bladder urothelium to form intracellular bacterial communities (IBCs). These IBCs dissociate and bacteria flux out of bladder facet cells, some with filamentous morphology, and ultimately establish quiescent intracellular reservoirs that can seed recurrent infection. This IBC pathogenic cycle has not yet been investigated in humans. In this study we sought to determine whether evidence of an IBC pathway could be found in urine specimens from women with acute UTI.Methods and FindingsWe collected midstream, clean-catch urine specimens from 80 young healthy women with acute uncomplicated cystitis and 20 asymptomatic women with a history of UTI. Investigators were blinded to culture results and clinical history. Samples were analyzed by light microscopy, immunofluorescence, and electron microscopy for evidence of exfoliated IBCs and filamentous bacteria. Evidence of IBCs was found in 14 of 80 (18%) urines from women with UTI. Filamentous bacteria were found in 33 of 80 (41%) urines from women with UTI. None of the 20 urines from the asymptomatic comparative group showed evidence of IBCs or filaments. Filamentous bacteria were present in all 14 of the urines with IBCs compared to 19 (29%) of 66 samples with no evidence of IBCs (p < 0.001). Of 65 urines from patients with E. coli infections, 14 (22%) had evidence of IBCs and 29 (45%) had filamentous bacteria, while none of the gram-positive infections had IBCs or filamentous bacteria.ConclusionsThe presence of exfoliated IBCs and filamentous bacteria in the urines of women with acute cystitis suggests that the IBC pathogenic pathway characterized in the murine model may occur in humans. The findings support the occurrence of an intracellular bacterial niche in some women with cystitis that may have important implications for UTI recurrence and treatment.

Partial Text: Urinary tract infections (UTIs) affect nearly 13 million women annually in the United States alone and can result in significant costs and morbidity [1–5]. Uropathogenic Escherichia coli (UPEC) is the predominant causative agent, responsible for up to 85% of community-acquired infections [6,7]. The majority of UTIs are thought to arise when uropathogens present in the fecal flora colonize the vaginal introitus, ascend into the bladder, and initiate a host response manifested by secretion of cytokines, pyuria, and the onset of symptoms [8].

Our study provides evidence that episodes of E. coli cystitis in humans may involve an IBC pathogenic pathway similar to that observed in mice. Evidence of filamentous bacteria and exfoliated bladder facet cells containing large collections of E. coli were observed by light microscopy and confirmed by immunofluorescence. High-resolution electron microscopy showed large biofilm-like IBCs and long filamentous bacteria. The expected variety of uropathogens [6] was cultured from infected women in the study, yet IBCs and filaments were not observed in urines from women infected with gram-positive pathogens or in urines from asymptomatic women. Additionally, the urine cytologies observed in human and murine UTIs were indistinguishable.



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