The Antimicrobial Defense Mechanism of the Female Urethra: A Reassessment

Abstract

This review of the literature and study of the cytology of the urethra were done to define the potential role of the female urethra as a staging site for urinary tract infection and examine the evidence for a urethral defense mechanism. We re-analyzed data on the quantitative microbiology of the female urethra published 3 decades ago, reviewed the literature on the initiation of ascending urinary tract infections, the cytology and anatomy of the urethra, and performed studies of the morphology of urethral cells in boys and girls, men, menstruating and menopausal women, and women with acute cystitis. We also considered clues about the urethral microenvironment provided by gonococcal cervicitis and urethritis. We found strong statistical evidence that the female urethra has a powerful antimicrobial defense mechanism, which appears to differ in women with and without recurrent urinary tract infections. We corroborated the findings of previous investigators that the female urethra is lined by cells identical to those of the vagina that respond similarly to estrogens. We found immature basal and parabasal cells in children, and a modest inflammatory response to urinary tract infection. The female urethra may provide a favorable environment for colonization by uropathogens but it is protected by a powerful defense mechanism. This mechanism may be explained by the shedding of uropathogens bound to exfoliating urethral cells, trapping of bacteria by mucus secreted by the paraurethral glands, intermittent washout by urine, local production of Ig, cytokines and defensins and mobilization of leukocytes.