Cystitis — what mechanism is attributed to cranberry juice?

• A. Increases urine acidity
• B. Directly kills bacteria
• C. Proanthocyanidins interfere with bacterial adhesion
• D. Reduces urine volume

Answer: (C)

Cranberry juice helps prevent cystitis primarily by blocking bacterial adhesion to the urinary tract lining. The active compounds, A-type proanthocyanidins, interfere with the ability of bacteria—especially E. coli—to attach to urothelial cells via fimbriae (adhesion structures). When bacteria can’t stick, they’re less likely to colonize and ascend into the bladder, reducing infection risk. This anti-adhesion action is why cranberry is considered preventive rather than bactericidal. It does not rely on killing bacteria directly, nor does it reliably rely on acidifying urine or reducing urine volume, which are not the primary mechanisms at work.