The therapeutic workings of cranberry in the urinary tract and beyond

Urinary tract infections (UTIs), defined as the presence of bacteria in the urine at elevated levels (> 100 000/mL), are highly prevalent across the population.^1,2 They are particularly common in women, with approximately 40-50% of women experiencing at least one episode during their lifetime and 20-30% having recurrent UTI’s.^1,3 The recommended treatment protocol for recurrent UTIs is antibiotic therapy, and while this is generally an effective approach, the over-use of antibiotics is associated with the development of antimicrobial resistance.^1,4 Cranberry, with its ability to reduce bacterial adhesion on the urinary tract wall, is a nutritional approach to recurrent UTIs, without the risk of antimicrobial resistance. A significant body of evidence has elucidated the specific mechanisms underlying cranberry’s beneficial effect on urinary tract infections and health.

Urinary tract mode of action

For an endogenous bacterial infection to develop and progress, a necessary initial step is for the pathogenic bacteria to adhere to a mucosal surface. E. coli-induced UTIs follow this pathophysiological process by utilising fimbriae (fine projections on the bacterial surface) with adhesion components to attach to urinary tract epithelial cell receptors. Bacterial proliferation subsequently takes place, resulting in elevated levels of pathogenic E. coli in the urine and the onset of associated symptoms.⁵

Research has clearly demonstrated the importance of the A-type proanthocyanidins (PACs) constituents and their metabolites in cranberry extracts for effectively treating urinary tract infections due to mechanisms they uniquely exhibit. Specifically, A-type PACs inhibit the pathogenic fimbriated E. coli bacteria from adhering to the mucosal surface of the bladder and urethra, preventing bacterial colonisation and subsequent infection.^5-8

This involves several mechanisms including:

• competitive inhibition
• fimbrial expression, synthesis or attachment prevention
• bacterial morphology alteration
• reduction in biofilm formation
• influence of quorum sensing processes.^5,7,9,10

Cranberry and the gut relationship

Beyond these well-established mechanisms, cranberry (A-type PACs and their metabolites) has also been shown to beneficially modulate the gastrointestinal microbiome composition (reducing Enterobacteriaceae levels and increasing the abundance of Bacteroidaceae populations), counteracting the impact of an animal-based diet on the microbiota, bile acids, and short chain fatty acids, while supporting impaired gastrointestinal mucosal barrier integrity and immunity.^{7, 10-12}

Additionally, merging evidence shows that the intestine is a reservoir for uropathogenic bacteria with cranberry metabolites potentially interacting with extra-intestinal E. coli and decreasing its intestinal colonisation, consequently reducing the risk of UTI incidence.¹²

The combination of mechanisms that target several pathogenic processes of UTI-causing bacteria and promoting gastrointestinal health highlights the comprehensive efficacy of cranberry for supporting urinary tract health in different population groups.