Repeat calcium oxalate stones cut by 70% when bacterium is present.


Colonization with Oxalobacter formigenes may reduce the risk of calcium oxalate kidney stones, a study suggests.

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O. formigenes is a gram-negative anaerobic bacterium that metabolizes oxalate in the intestinal tract. Up to 80% of kidney stones are made predominately of calcium oxalate (CaOx).


David W. Kaufman, ScD, of the Slone Epidemiology Center at Boston University, and his colleagues conducted a case-control study involving 247 adult patients with recurrent calcium oxalate stones and 259 age-, gender-, and region-matched controls. The investigators determined O. formigenes prevalence by stool culture.


The bacterium was present in 17% of the stone formers and 38% among controls, the authors noted in the Journal of the American Society of Nephrology (2008; published online ahead of print). After adjusting for age, gender, education, race, region, dietary oxalate, antibiotic use, and family history of stones, the presence of O. formigenes was associated with a 70% lower risk of recurrent CaOx stones.


In a subgroup of subjects who completed a 24-hour urine collection, the risk for kidney stones was directly proportional to urinary oxalate. “Surprisingly, median urinary oxalate excretion did not differ with the presence or absence of O. formigenes colonization,” the authors noted.


Dr. Kaufman’s group observed an increase in the prevalence of O. formigenes with increasing oxalate consumption, which the researchers said is expected “because dietary oxalate is a major energy source for this bacterium, along with oxalate from endogenous production. This relation was not observed in the case patients, however, and there is no clear explanation for the latter finding.”


“Our findings are of potential clinical importance,” Dr. Kaufman’s group wrote. “O. formigenes is a naturally occurring bacterium that has no known adverse effects. CaOx renal stones are a recurring health problem that causes substantial morbidity and use of health care resources…The possibility of using the bacterium as a probiotic is in the early stages of investigation.”


The researchers cited a recent trial involving patients with primary hyperoxaluria. Among 16 patients treated with O. formigenes as a frozen paste or enteric-coated capsules, 11 showed a reduction in urinary or plasma oxalate.