How do cranberries prevent urinary tract infection?

Researchers from Worcester Polytechnic Institute, in Massachusetts went into the lab to seek the answer.

First, the details.

  • Atomic force microscopy was used to study the adhesion forces between Escherichia coli and a model surface (silicon nitride).
  • The objective was to determine the effect of cranberry products to change the ability of bacterial to adhere to the surface.
  • Bacteria were grown in tryptic soy broth supplemented with either light cranberry juice cocktail or cranberry proanthocyanidins (PACs; have antioxidant properties).

And, the results.

  • Longer exposure of the bacteria to either the cranberry juice or the PACs resulted in a greater decrease in bacterial attachment to the surface.

The bottom line?
Assuming that silicon nitride is appropriate for this research, the results indicate that chemicals present in cranberries — and not the acidity of cranberry juice, as previously thought — prevent infection-causing bacteria from attaching to the cells that line the urinary tract.

Studies in patients supporting the use of cranberries are summarized here, here, here, and here.

3/12/09 20:56 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.