Cranberries Impede Antibiotic Resistance

The global spread of antibiotic resistance is undermining decades of progress in fighting bacterial infections. Due to the overuse of antibiotics in medicine and agriculture, we are on the cusp of returning to a pre-antibiotic era in which minor infections can once again become deadly.

Cranberries, which are highly sought after for their tangy taste and antioxidants, may also help fight bacteria, according to a study published today in Advanced Science. When treated with molecules derived from cranberries, pathogenic bacteria become more sensitive to lower doses of antibiotics. What’s more, the bacteria don’t develop resistance to the antibiotics.

Given the popular belief that drinking cranberry juice is helpful against urinary tract infections, the researchers sought to find out more about the berry’s molecular properties by treating various bacteria with a cranberry extract. The bacteria selected for study were those responsible for urinary tract infections, pneumonia, and gastroenteritis: Proteusmirabilis, Pseudomonasaeruginosa, and Escherichiacoli.

“Normally when we treat bacteria with an antibiotic in the lab, the bacteria eventually acquire resistance over time,” says senior author Nathalie Tufenkji of McGill University. “But when we simultaneously treated the bacteria with an antibiotic and the cranberry extract, no resistance developed.”

Analyses showed that the cranberry extract increases bacterial sensitivity to antibiotics by acting in two ways: First, it makes the bacterial cell wall more permeable to the antibiotic, and second, it interferes with the mechanism used by the bacteria to pump out the antibiotic. Consequently, the antibiotic penetrates more easily, and the bacteria have a harder time getting rid of it.

“The activity is generated by molecules called proanthocyanidins,” says coauthor Éric Déziel of INRS. “There are several different kinds of proanthocyanidins, and they may work together to deliver this outcome. We’ll need to do more research to determine which ones are most active in synergy with the antibiotic.”

The pattern also persisted inside living fruit flies. If the results are also confirmed in animals, certain classes of antibiotics subject to high levels of resistance could be made useful again by using cranberry extract to boost their potential.

“We are eager to pursue this research further,” says Tufenkji. “Our hope is to reduce the doses of antibiotics required in human and veterinary medicine as part of efforts to combat antibiotic resistance.”