In vitro degradation of oxalic acid by human feces

Oxalic acid-degrading bacteria have been isolated from human faces. Therefore, the possibility exists that oxalic acid in food is degraded in human intestine by such bacteria, and absorption and excretion of oxalic acid is reduced. It may be possible that patients who form idiopathic stones have fewer oxalic acid-degrading bacteria than healthy controls. The purpose of this study is to examine the possibility that oxalic acid in food is degraded in the human intestine.

Nineteen patients with calcium stones and 13 healthy subjects were included in the study. Samples of feces were diluted with Barber medium containing 1 g/L of oxalic acid dihydrate, and 1%, 0.1% and 0.01% suspensions were prepared. These solutions were incubated under anaerobic conditions at 37 degrees C for seven days. The degradation of oxalic acid was estimated by the decrease of oxalic acid in the medium.

The feces of almost all persons with or without calculi degraded oxalic acid to some degree. Incomplete or no oxalic acid degradation was found in 15 of the 19 stone-forming patients and in five of the 13 stone-free controls.

Large numbers of oxalic acid-degrading bacteria were observed less often in the feces of stone-formers than in the feces of stone-free controls.