Cranberry works by preventing microorganisms from adhering to the epithelial cells that line the urinary tract, and not by acidifying the urine, as was once believed. Escherichia coli, the most common UTI-causing bacteria, produces chemicals that enable the organism to cling to epithelial cells where they proliferate and cause infection. Cranberry has been found to contain two substances that inhibit the adhesion activity of bacteria: fructose and an, as yet, unidentified polymeric compound.
