Cranberry juice creates energy barrier that keeps bacteria away from cells
Results help explain how cranberry juice can prevent urinary tract infections
For generations, people have consumed cranberry juice,
convinced of its power to ward off urinary tract infections, though the exact
mechanism of its action has not been well understood. A new study by researchers
at Worcester Polytechnic Institute (WPI) reveals that the juice changes the
thermodynamic properties of bacteria in the urinary tract, creating an energy
barrier that prevents the microorganisms from getting close enough to latch onto
cells and initiate an infection.
The study, published in the journal Colloids and Surfaces: B, was conducted
by Terri Camesano, associate professor of chemical engineering at WPI, and a
team of graduate students, including PhD candidate Yatao Liu. They exposed two
varieties of Escherichia. coli bacteria, one with hair-like projections known as fimbriae
and one without, to different concentrations of cranberry juice. Fimbriae are
present on a number of virulent bacteria, including those that cause urinary
tract infections, and are believed to be used by bacteria to form strong bonds
with cells.
For the fimbriaed bacteria, they found that even at low concentrations,
cranberry juice altered two properties that serve as indicators of the ability
of bacteria to attach to cells. The first factor is called Gibbs free energy of
attachment, which is a measure of the amount of energy that must be expended
before a bacterium can attach to a cell. Without cranberry juice, this value was
a negative number, indicating that energy would be released and attachment was
highly likely. With cranberry juice the number was positive and it grew steadily
as the concentration of juice increased, making attachment to urinary tract
cells increasingly unlikely.
Surface free energy also rose, suggesting that the presence of cranberry
juice creates an energy barrier that repels the bacteria. The researchers also
placed the bacteria and urinary tract cells together in solution. Without
cranberry juice, the fimbriaed bacteria attached readily to the cells. As
increasing concentrations of cranberry juice were added to the solution, fewer
and fewer attachments were observed.
Cranberry juice had no discernible effect on E. coli bacteria without fimbriae, suggesting that compounds in the juice may act directly on the
molecular structure of the fimbriae themselves. This reinforces previous work by
the WPI team that showed that exposure to cranberry juice alters the shape of
the fimbriae, causing them to become compressed. Using an atomic force
microscope as a minute strain gauge, the team also showed that the adhesive
force exerted by bacteria on urinary tract cells declined in direct proportion
to the concentration of cranberry juice in the solution.
"Our results show that, at least for urinary tract infections, cranberry
juice targets the right bacteria—those that cause disease—but has no effect on
non-pathogenic organisms, suggesting that cranberry juice will not disrupt
bacteria that are part of the normal flora in the gut," Camesano says. "We have
also shown that this effect occurs at concentrations of cranberry juice that are
comparable to levels we would expect to find in the urinary tract."
Camesano notes that unpublished work has shown that while cranberry juice has
potent effects on disease-causing bacteria, those effects are transitory. "When
we takes E. coli. bacteria that have been treated with cranberry juice and place
them in normal growth media, they regain the ability to adhere to urinary tract
cells," she says. "This suggests that to realize the antibacterial benefits of
cranberry, one must consume cranberry juice regularly—perhaps daily."
For those watching calories, Camesano says other recent work in her lab has
shown that the effects of regular cranberry juice cocktail and diet (sugar-free)
cranberry juice are identical. "That's good news for people who do not like to
consume a lot of sugary juice," she says.- WPI
More information:
 Michael Dorsey
mwdorsey@wpi.edu
508-831-5609
Worcester Polytechnic Institute
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