Urinary oxalate levels and the enteric bacterium Oxalobacter formigenes in patients with calcium oxalate urolithiasis

Objectives: We performed a prospective study to evaluate the intestinal colonization of Oxalobacter formigenes and its relationship with urinary oxalate levels in patients with calcium oxalate stone disease. Methods: One hundred and three patients with calcium oxalate urolithiasis, ranging in age from 21 to 73 years (mean age, 47 years) who were followed from August 2000 to September 2001 participated in this study. Fresh stool and 24-hour urine samples were collected. Genus specific oligonucleotide sequences corresponding to the homologous regions residing in the oxc gene were designed. In order to quantify O. formigenes in clinical specimens, a quantitative-PCR-based assay system utilizing a competitive DNA template as an internal standard was developed. Urine volume, pH, creatinine, oxalate, calcium, magnesium, phosphate, citrate and uric acid were measured. Results: Intestinal Oxalobacteria were detected in 45.6% (n = 47) of calcium oxalate stone patients by PCR. In stone formers who tested negative for Oxalobacteria, the average urinary oxalate level was 0.36 mmol/day, and this compared to 0.29 mmol/day for those patients that tested positive for Oxalobacteria (p < 0.05). Mean colony forming units per gram of stool of all patients was 1.1 x 10(7) (0-4.1 x 10(8)), and the level of 24 hours urine oxalate significantly decreased with increasing level of colony forming units of O. formigenes (r = -0.356, p = 0.021). Conclusion: Our results support the concept that O. formigenes is important in maintaining oxalate homeostasis and that its absence from the gut may be the risk of calcium oxalate urolithiasis. (C) 2003 Elsevier B.V. All rights reserved.