Urinary Tract Infection - Causes

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Factors in Overcoming the Bacterial Defense Systems

The bacteria that cause most UTIs are very common and nearly everyone harbors them. It is not clear how they proliferate and break down the natural defenses of the body. Among the possible ways this occurs are:

Changes in the Acid-Alkaline Balance of the Urinary Tract. Changes in the amount or type of acid within the genital and urinary tracts are major contributors to lowering the resistance to infection. For example, beneficial organisms called lactobacilli increase the acidic environment in the urinary tract. Reductions in their number (which, for example, occurs with estrogen loss after menopause), increases pH and therefore the risk of infection.

Biofilm. One theory, called the biofilm mode of growth, suggests that sometimes bacteria form capsules that adhere to the urinary tract, which protects them from many of the body's normal defenses.

Review Date: 06/16/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital