Microbial Etiology of Urinary Tract Infections (UTI)

The microbial etiology of urinary tract infections (UTI) has been regarded as well-established and reasonably consistent.


  1. Escherichia coli: The majority of community-acquired symptomatic UTIs in elderly women are caused by E coli. E. coli remains the predominant uropathogen (80%) isolated in acute community-acquired uncomplicated Urinary Tract infections.
  2. Staphylococcus saprophyticus (10% to 15%)
  3. Klebsiella,
  4. Enterobacter,
  5. Proteus species

Other pathogens (comparatively rare)

  1. Streptococcus agalactiae
  2. Psuedomonas
  3. Enterococci infrequently cause uncomplicated cystitis and pyelonephritis.

The etiology of UTI is also affected by underlying host factors that complicate UTI, such as

  1. Age: The most common organisms isolated in children with uncomplicated UTI are Enterobacteriaceae. Gram-positive organisms are common, and polymicrobial infections account for up to 1 in 3 infections in the elderly.
  2. Gender: Women are affected more often than men (about 40 to 50 times), because of shorter female urethra (4 cm) compared with male urethra (20 cm) i.e. infectious agents reach the bladder more easily in female.
  3. Diabetes: Etiologic pathogens associated with UTI among patients with diabetes include Klebsiella spp., Group B streptococci, and Enterococcus spp., as well as E coli.
  4. Spinal cord injury or urinary catheterization: Patients with spinal cord injuries commonly have E coli infections.

Complicated vs. Uncomplicated UTI:

Complicated UTI has a more diverse etiology than uncomplicated UTI, and organisms that rarely cause disease in healthy patients can cause significant disease in hosts with anatomic, metabolic, or immunologic underlying disease.