Kaufman DW et al. (2008) Oxalobacter formigenes may reduce the risk of calcium oxalate kidney stones. J Am Soc Nephrol [doi:10.1681/ASN.2007101058]

Oxalobacter formigenes is a Gram-negative, anaerobic bacterium that breaks down oxalate in the colon. Small studies have suggested that the absence of O. formigenes might result in increased urinary oxalate levels and, thus, lead to the formation of calcium oxalate kidney stones. Kaufman et al. have determined, in a large population, that lack of O. formigenes colonization is associated with an increased risk of kidney stone formation but not necessarily with urinary oxalate excretion.

This case–control study included 247 patients (aged 18–69 years) who were being treated for calcium oxalate stones at a urology practice at one of four hospitals in the US from January 2004 to August 2006, and 259 controls without stone disease who were matched for age, sex and geographical region. The participants' stool samples were collected and cultures were grown in an O. formigenes-selective medium. Presence of the bacterium was then determined by use of an oxalate precipitation assay.

O. formigenes colonization was less prevalent among patients with kidney stones than among controls (17% vs 38%, multivariate odds ratio 0.3, 95% CI 0.2–0.5). This relationship was consistent regardless of age, sex, ethnicity, region, dietary oxalate consumption or previous use of antibiotics. Among a subset of participants who submitted 24 h urine samples (139 patients and 138 controls), urinary oxalate levels were positively associated with an increased risk of developing kidney stones (Ptrend = 0.002); however, urinary oxalate levels were not related to the presence or absence of O. formigenes.