Appl Environ Microbiol
Cranberry juice gives UTI antibiotic a boost
Clinical takeaway: Findings support continued interest in natural adjuvants for existing antibiotics.
Rising antibiotic resistance has renewed interest in compounds that amplify existing drugs without requiring the development of new ones. This study tested whether cranberry juice could enhance fosfomycin activity against clinical E. coli isolates and limit the spontaneous resistance that frequently emerges in laboratory testing.
Cranberry juice both strengthened the antibiotic effect and made resistance far less likely to develop in lab cultures. Across 32 clinical isolates of uropathogenic E. coli (UPEC), the juice significantly increased fosfomycin growth-inhibition activity in 72% of strains. It also suppressed spontaneous resistance dramatically: the frequency of resistant colonies fell by up to five orders of magnitude, and at higher fosfomycin concentrations, no resistant colonies emerged at all on juice-containing plates. One isolate that was fully resistant to fosfomycin alone became sensitive in the juice's presence.
Whole-genome sequencing pointed to a mechanism. Fosfomycin enters E. coli through two sugar-transport systems, glycerol-3-phosphate transporter (GlpT) and hexose 6-phosphate uptake transporter (UhpT). Without juice, resistant mutants typically carried glpT mutations; with juice, mutations clustered in uhpT or related regulatory genes. Reporter assays showed that cranberry juice essentially shut down glpT expression while leaving UhpT-mediated uptake intact, sustaining antibiotic entry through the alternative route. That shift may explain both the enhanced activity and the lower rate of resistance.
The findings give mechanistic plausibility to long-standing associations between cranberry and UTI prevention. Identifying which juice constituents drive the effect, and whether they survive ingestion to reach the urinary tract at active levels, remains the next step. The work was funded by the Cranberry Institute.
"We don't know if the metabolites will reach the infection," said senior author Eric Déziel, PhD, microbiologist at the Institut National de la Recherche Scientifique in Montreal. He later added, "With the challenge of the multi-drug resistance, we need to work from many different directions."
Source: Groleau MC. Appl Environ Microbiol. 2026 May 4. Cranberry juice potentiates sensitivity of uropathogenic Escherichia coli (UPEC) strains to fosfomycin and decreases occurrence of spontaneous resistance