Objective <p>To evaluate the efficacy of fosfomycin trometamol powder (FMT) in preventing biofilm-associated bacterial infections on double-J stents in diabetic patients; to characterize the species distribution and antimicrobial susceptibility patterns of biofilm-forming bacteria isolated from these devices; and to identify clinical and microbiological risk factors associated with such infections—thereby informing evidence-based strategies for infection prevention in this high-risk population.</p> Methods <p>A total of 100 adult diabetic patients who underwent double-J stent placement at our tertiary care center between June 2024 and June 2025 were prospectively enrolled and randomized in a 1:1 ratio to either an experimental group or a control group (<i>n</i> = 50 per group). Patients in the experimental group received a single oral dose of 3&#xa0;g FMT on the day before stent insertion and on postoperative days 7 and 15; those in the control group received a single oral dose of 0.5&#xa0;g levofloxacin (LFX) tablets on the day before stent insertion and on postoperative days 1 and 2. At the time of stent removal, stent surface specimens were collected for quantitative biofilm-forming bacterial culture, species identification, and antimicrobial susceptibility testing. Baseline clinical characteristics, stent-related symptoms, and infection outcomes were systematically recorded. Statistical analysis was conducted using SPSS version 26.0, with two-sided <i>p</i> &lt; 0.05 considered statistically significant.</p> Results <p>Among the 100 diabetic patients with indwelling double-J stents, biofilm-forming bacterial colonization was detected in 24 (24.0%), with significantly lower prevalence in the experimental group (7/50, 14.0%) than in the control group (17/50, 34.0%) (<i>χ</i>² = 5.48, <i>p</i> = 0.019). <i>Escherichia coli</i> (<i>E. coli</i>) was the predominant pathogen isolated (accounting for 50% of all positive cultures); among these <i>E. coli</i> isolates, 83.3% (10/12) were confirmed as extended-spectrum <i>β</i>-lactamase (ESBL)-producing strains. Gram-negative bacilli exhibited high-level resistance to ciprofloxacin (93.7%), ampicillin (100%), levofloxacin (87.5%), cefepime (68.7%), cefazolin (87.5%), cefuroxime (81.2%), and ceftriaxone (75.0%). Multivariable logistic regression identified age ≥ 60&#xa0;years, double-J stent indwelling duration ≥ 30&#xa0;days, daily fluid intake ≤ 2000&#xa0;mL, serum albumin &lt; 30&#xa0;g/L, serum creatinine &gt; 110&#xa0;μmol/L, and glycated hemoglobin (HbA1c) &gt; 6% as independent risk factors for biofilm-associated bacterial infection (p &lt; 0.05).</p> Conclusion <p>When administered with equivalent dosing frequency (three doses total), FMT was associated with a significantly lower detection rate of biofilm-forming bacteria in double-J stent specimens compared with LFX among diabetic patients. These findings support the preferential use of FMT over LFX for targeted prophylaxis in high-risk diabetic populations and underscore the importance of integrating antimicrobial stewardship—particularly agent selection aligned with local resistance patterns—with proactive management of modifiable risk factors to optimize infection prevention and clinical outcomes.</p>