In laboratory experiments, researchers in a recently published study investigated whether cranberry juice could increase the effectiveness of fosfomycin against uropathogenic Escherichia coli and limit the development of antibiotic resistance.
The findings, published in Applied and Environmental Microbiology, offer a different direction for cranberry research, which has largely focused on preventing bacteria from adhering to the urinary tract. However, the study did not test the combination in humans.
The Cranberry Institute funded the research and provided the cranberry juice used in the experiments.
A different role for cranberry
Researchers tested cranberry juice in combination with fosfomycin, a broad-spectrum antibiotic primarily prescribed to treat uncomplicated lower urinary tract infections (bladder infections) in women, against 32 UTI-associated E. coli strains.
“Our results showed that cranberry juice potentiates fosfomycin activity against most UPEC isolates tested,” the researchers wrote.
The team then explored what could be driving the effect. Fosfomycin relies on transport systems to enter bacterial cells, and the results pointed to changes in one of the pathways involved in antibiotic uptake.
According to researchers, this differs from the mechanism more commonly associated with cranberry and urinary tract health. A-type proanthocyanidins (PACs) in cranberries have been studied for their ability to interfere with bacterial adhesion to the urinary tract.
Tracy Gensler, MS, RD, nutrition science communications lead at Pollock Communications, told NutraIngredients that the findings could add another area of investigation without changing the existing understanding of cranberry PACs.
“This warrants additional research to examine this benefit and to further elucidate the mechanism of action, but it doesn’t change the well-established role of cranberry PACs in helping to prevent UTIs,” she said.
The researchers also assessed whether cranberry juice affected the emergence of fosfomycin resistance. Under some of the laboratory conditions tested, adding cranberry juice reduced the emergence of resistant bacteria by more than 100,000-fold.
The researchers said the findings “suggest that cranberry juice may help suppress the emergence of fosfomycin resistance.”
Questions remain for human use
The study was conducted in vitro, leaving open the question of whether the interaction would occur when cranberry juice and fosfomycin are consumed by people.
“It’s too soon to establish a connection between drinking cranberry juice and the potency of fosfomycin or other antibiotics, and further research is needed,” Gensler said.
There are also questions about what in the cranberry juice produced the effect. The researchers did not identify the responsible compounds, leaving it unclear whether the findings could extend to cranberry extracts or other dietary supplement formulations.
“More research is definitely needed to inform product development,” Gensler added.
The study only investigated fosfomycin, so it also remains unknown whether cranberry could interact similarly with other antibiotics used to treat UTIs.
Gensler said the research could pave the way for studies pairing cranberry with other antibiotics, but cautioned that those potential benefits are not yet known.
Source: Applied and Environmental Microbiology. doi: 10.1128/aem.02521-25. “Cranberry juice potentiates fosfomycin activity against uropathogenic scherichia coli”. Authors: Groleau, M. et al.
