Urinary Tract Infection, UTI - Pathogenesis, Route of Infection

Pathogenesis of Urinary Tract Infection (UTI)

Route of infection

Bacteria can invade and cause a Urinary Tract Infection (UTI) via 3 major routes:

• Ascending route

• Hematogenous route

• Lymphatic pathway

Ascending route

It is the most common course of infection in females. But mostly it is associated with instrumentation (eg. urinary catheterization, cystoscopy) and is the most common cause of hospital-acquired Urinary Tract Infection (UTI) in both sexes.

For Urinary Tract Infection (UTI) to occur by the ascending pathway, enteric gram-negative bacteria and other microorganisms that originate in the Gastro-Intestinal (GI) tract must be able to colonize the vaginal cavity or the periurethral area.

Once these organisms gain access to the bladder, they may multiply and then pass up to the ureters to the kidneys. Both sexual activity and anatomical design (short urethra and its proximity to anus) in females contribute to increased causes of Urinary Tract Infection (UTI).

In hospitalized patients, soon patients are colonized with bacteria endemic to the institution, often gram-negative aerobic and facultative bacilli carrying resistance markers. These bacteria colonize patients' skin, GI tract, and mucous membranes including the anterior urethra.

With the insertion of a catheter, bacteria may be pushed along the urethra into the bladder. Infection may occur with an indwelling catheter, migrating along the track between the catheter and urethral mucosa, and gaining access to the bladder. Approximately 10-30% of catheterized patients will develop bacteriuria.

Hematogenous route

Urinary Tract Infection (UTI) may also occur by the hematogenous or blood-borne route. The hematogenous spread usually occurs as a result of bacteremia. Any systematic infection can lead to seeding of the kidneys, but only certain microorganisms such as S. aureus or Salmonella spp. are invasive.

The presence of yeast (usually Candida albicans), Mycobacterium tuberculosis, Salmonella spp., Leptospira spp., or S. aureus in the urine often indicates pyelonephritis acquired via hematogenous spread or the descending route. Hematogenous spread accounts for 5% of Urinary Tract infections (UTI).

Lymphatic pathway

Urinary Tract Infection (UTI) through this pathway may be the result of increased pressure on the bladder that causes the lymphatic flow to the kidneys.