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The Female Microbiome & Urinary Tract Infections | Research

Urinary Tract Infections (UTIs) can be divided into upper tract infections, which involve the kidneys (pyelonephritis), and lower tract infections, which involve the bladder (cystitis), urethra (urethritis), and prostate (prostatitis). Infection may spread from one site to the other. Although urethritis and prostatitis are infections that involve the urinary tract, the term UTI usually refers to pyelonephritis and cystitis (1).


Urinary tract infections (UTIs) are more common in women than men, with one third of women having at least one infection at some point in their life (2). The infection can occur at different sites in the urinary tract, including the bladder, kidneys, ureters, and the urethra.

Most UTIs are caused by bacteria that enter the urethra and then the bladder. These include E. coli, P. mirabilis, S. saprophyticus, P. aeruginosa, E. faecalis and Klebsiella (3-5).

The bladder epithelium has natural defences such as surface mucopolysaccharides which prevent small numbers of bacteria adhering to the bladder wall and increase the likelihood of the bacteria being flushed out during urination. Urine osmolality and pH, as well as urea also inhibit bacterial growth (6).


Urinary pathogens have several means of invading the host, including adherence to host cells with adhesins, toxin production and immune evasion (5). Once adhered, the growing bacterial population triggers an inflammatory response and neutrophil invasion. It is these bacterial toxins, enzymes and metabolites that are released from dead neutrophils that can irritate the epithelial lining of the bladder and urethra, which causes the typical symptoms of pain during urination, frequent urination or the urge to urinate, fever and flank pain (7).

Risk Factors

Women tend to get UTIs more often than men because their urethra is shorter and closer to the anus. Because of this, women are more likely to get an infection during sexual activity or when using a contraceptive diaphragm. Menopause and pregnancy also increase the risk of getting a UTI (7).

Anatomical, or functional abnormalities in the urinary tract, illness, immunodeficiency and catheterisation are also risk factors (6). Urinary retention is a common problem among the elderly, and UTIs are the most common infection in care home residents, with the standard treatment being catheterisation, which can also cause a UTI (8). The pathogens associated with catheter-related UTIs are E. coli, P. aeruginosa, Klebsiella, Enterobacter and Candida spp. (9).

UTI Associations

UTIs affect all ages and genders and can cause a dramatic decrease in the quality of life. They have several local and systemic associations, including:

  • Pyelonephritis
  • Sepsis and endotoxemia
  • Vaginal and genital infections
  • Gastrointestinal co-morbidities
  • Pregnancy complications, including pre-term delivery

  1. Imam TH. Introduction to urinary tract infections. Merck Manual; 2013.
  2. Ikaheimo R, Siitonen A, Heiskanen T, et al. Recurrence of urinary tract infection in a primarycare setting: analysis of a 1-year follow-up of 179 women. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America 1996;22:91-9.
  3. Flores-Mireles AL, Walker JN, Caparon M, Hultgren SJ. Urinary tract infections: epidemiology, mechanisms of infection and treatment options. Nat Rev Microbiol 2015;13:269-84.
  4. Mehnert-Kay SA. Diagnosis and management of uncomplicated urinary tract infections. Am Fam Physician 2005;72:451-6.
  5. Nielubowicz GR, Mobley HL. Host-pathogen interactions in urinary tract infection. Nat RevUrol 2010;7:430-41.
  6. Westran Sa. Clinical Bacteriology. 2nd Edition ed: Manson Publishing Ltd: 135-142; 2005
  8. D'Hondt F, Everaert K. Urinary tract infections in patients with spinal cord injuries. Curr Infect Dis Rep 2011;13:544-51.
  9. Vergidis P, Patel R. Novel approaches to the diagnosis, prevention, and treatment of medical device-associated infections. Infect Dis Clin North Am 2012;26:173-86.

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