Cranberry Juice Could Help Antibiotics Fight UTIs

More than 400 million people experience a urinary tract infection every year, and some epidemiological studies estimate that more than half of all women will develop at least 1 in their lifetime. Most UTIs are caused by pathogenic strains of Escherichia coli bacteria, and the antibiotic fosfomycin is often prescribed as the first line of treatment. However, increasing resistance to antibiotics is driving a search for alternative approaches to treatment.

New findings suggest that cranberry juice may lend a helping hand to antibiotics-at least on lab-grown strains. This week in Applied and Environmental Microbiology, researchers report that in 72% of uropathogenic E. coli strains tested, cranberry juice both boosted the antibiotic activity of fosfomycin and suppressed the emergence of mutations related to resistance. The work is promising but preliminary, noted lead author and microbiologist Eric Déziel, Ph.D, at the Institut National de la Recherche Scientifique in Montreal, Canada. 

The study doesn’t show, for example, if cranberry juice confers the same benefits after consumption. “We don’t know if the metabolites will reach the infection,” he said. But if they could, he said, then juice may increase the efficacy of antibiotic treatment. Future studies would be needed to determine how much cranberry juice would confer any benefit. 

Cranberry juice has long been regarded as a kind of folk remedy for preventing and treating urinary tract infections, said Déziel, but scientists originally attributed the benefit to the high acidity of the juice. More recent studies have linked its effect to compounds in the juice that can block bacteria from attaching to cells lining the urethra. Until now, however, researchers hadn’t examined its interactions with antibiotics. 

In the paper, the researchers describe how cranberry juice interacts with fosfomycin and bacteria. Fosfomycin enters bacterial cells through the same entry channels used by the microbes to acquire some sugars. Something in the cranberry juice-Déziel says the scientists aren’t yet sure what, exactly-induces the bacteria to increase its uptake of sugars within one of those channels, which means it also absorbs more fosfomycin. Resistance to antibiotics often results from mutations in genes associated with other nutrient channels. 

Déziel’s lab focuses on understanding communication between bacteria, and on identifying natural compounds that might disrupt that communication and point to new ways to treat dangerous infections. In previous lab studies, he and his collaborators found that cranberry extracts had a synergistic effect on the potency of antibiotics against resistant bacterial strains. 

Those findings caught the attention of the Cranberry Institute, which funds research aimed at understanding connections between cranberries and health, and funded the new study. They wanted to know whether cranberry juice had the same effect on bacteria as cranberry extracts. “It’s a very good question. People actually drink juice,” Déziel said. “They don't consume these very specific extracts.” 

Déziel noted that the new study doesn’t establish a connection between drinking juice and antibiotic potency, but it is promising enough to warrant more research. More importantly, he said, it supports the idea that natural compounds may be a useful frontier in fighting antibiotic resistance. Adjuvants that can bolster the efficacy of existing antibiotics are very promising because they don’t require the development of new drugs. “With the challenge of the multi-drug resistance," Déziel said, "we need to work from many different directions.”