Effect of Microbiome Modulation on Urinary Citrate and pH

Background: The gut microbiome plays an important role in the pathogenesis of urinary stone disease (USD), potentially through its influence on urinary components associated with stone formation. Changes in urinary pH and citrate levels are well established risk factors for USD. This study aims to determine the effects of microbiome suppression and subsequent restoration on urinary citrate concentration and pH, thereby elucidating the potential microbiome's contribution. Methods: Twenty-four male C57BL/6 mice were randomly assigned to receive placebo, sulfamethoxazole, or tylosin (n=8 per group). Baseline urine samples were collected over 24 hours prior to treatment initiation and again after one week of treatment. Antibiotics were subsequently discontinued, and the treated mice were co-housed with untreated mice for three weeks to allow microbiome restoration, after which a final urine sample was collected. Urinary citrate levels were measured using liquid chromatography–mass spectrometry (LC/MS) at the three timepoints, and urinary pH was assessed using a pH meter baseline and one week after antibiotic treatment. Results: Tylosin treatment significantly reduced urinary pH (6.72±0.35 to 5.93±0.34, p<0.01), whereas sulfamethoxazole had no significant effect (6.77±0.2 to 6.59±0.4, p=0.81) (Fig. 1). Urinary citrate excretion increased significantly in the sulfamethoxazole group (0.149±0.07 mg/24h to 0.404±0.16 mg/24h, p<0.01). Following co-housing with healthy mice, urinary citrate returned to its baseline value in both groups (Fig. 2). Conclusion: Antibiotic-induced suppression of the gut microbiome led to antibiotic-specific changes in urinary citrate levels and pH, both key factors influencing USD risk. Partial restoration of the healthy microbiome reversed these alterations in urinary citrate. Further studies are necessary to identify the specific bacterial species responsible for regulating urinary citrate excretion and acid-base balance. Funding: NIDDK Support