Get your juice on: Cranberries may limit bacterial antibiotic resistance, study finds

29 May 2019 --- Cranberry extract makes bacteria more sensitive to antibiotics, which may open new, promising avenues for limiting resistance to these drugs, say Canadian researchers. The findings showed that when treated with molecules derived from cranberries, pathogenic bacteria become more sensitive to lower doses of antibiotics and do not develop a resistance to them. The study was conducted at McGill University and L’Institut national de la recherche scientifique (INRS) in Canada and published in the journal Advanced Science.

“Normally when we treat bacteria with an antibiotic in the lab, the bacteria eventually acquire resistance over time,” says lead author, Nathalie Tufenkji, Chemical Engineering Professor at McGill. “But when we simultaneously treated the bacteria with an antibiotic and the cranberry extract, no resistance developed. We were very surprised by this, and we see it as an important opportunity.”

The extensive use of antibiotics in medicine and agriculture is promoting antibiotic resistance and undermining decades of progress in fighting bacterial infections. The danger lies in the fact that the world may return to an era in which minor infections can once again become deadly. Therefore, countering the fall in antibiotic efficacy by improving the effectiveness of currently available antibiotics is a crucial goal, the researchers say.

Cranberries are highly sought after for their tangy taste and the antioxidants they contain. In addition, it is a popular belief that drinking cranberry juice is helpful against urinary tract infections. 

Analyzing the berries
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 the study were those responsible for urinary tract infections, pneumonia and gastroenteritis (Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli).

Click to EnlargeCranberry extract increases bacterial sensitivity to antibiotics by acting in two ways, the analyses found. It makes the bacterial cell wall more permeable to antibiotics and interferes with the mechanism used by the bacteria to pump out the drugs. Consequently, the antibiotics penetrate more easily, and the bacteria have a harder time getting rid of it, which explains why the drug is effective at lower doses.

“These are really exciting results,” notes co-author Éric Déziel, a professor of microbiology at INRS. “The activity is generated by molecules called proanthocyanidins. 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 researchers also tested whether the pattern persisted in a preliminary animal model: infected insects. Since the synergistic effect of the extract and the antibiotic was also observed in the insects, further experiments will be conducted to clearly identify the active molecules.

If the results are 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,” Tufenkji says. “Our hope is to reduce the doses of antibiotics required in human and veterinary medicine as part of efforts to combat antibiotic resistance.”

Cranberries’ extensive health benefits
Research has shown that cranberries hold a number of beneficial health properties. From supporting urinary tract health to promoting a healthy gut microbiome. 

Recently, a new study published in American Chemical Society’s (ACS) Journal of Natural Products found that cranberry oligosaccharides can keep the bacteria responsible for urinary tract infections (UTIs) from adhering to the cells lining the urinary tract.

Researchers from the University of Wisconsin-Madison evaluated whether one simple addition to the diet – one handful a day of sweetened dried cranberries – could positively influence the gut microbiome. After just two weeks and with only ten subjects, the differences were statistically insignificant but according to the researchers, were moving in the right direction, pointing to a role for cranberries in improving gut health.

A Cranberry Institute and USDA-funded study into the potential protective effects of cranberries on the gut microbiome also found that adding cranberries to a meat-based diet can reduce the rise in secondary gut bile acids that have been associated with colon and GI cancer. The feeding trial – published in The Journal of Nutritional Biochemistry – found that the addition of whole cranberry powder to this common diet lessened potentially carcinogenic secondary bile acids and blunted the decline in beneficial short-chain fatty acids (SCFA) in the gastrointestinal (GI) tract.

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