To screen Oxalobacter formigenes (OxF) from fresh feces of healthy adults, and study its effect on the the prevention of calcium oxalate kidney stones.

OxF was screened and cultured from fresh feces of healthy adults. The rat model of calcium oxalate stone was established by esophageal gavage of 0.8% of ethylene glycol. Rats were divided into a control group and four groups of rats with ethylene glycol-induced calcium oxalate kidney stones according to random number table. Three groups were treated with 10⁶ CFU, 10⁷ CFU, 10⁸ CFU viable OxF every day, respectively, for 4 weeks. The blood and 24-hour urine samples were collected to detect the serum creatinine, urea nitrogen, serum and urine calcium, phosphorus, magnesium and urine oxalate every week. At the end of the 4th week, the rats were sacrificed and the kidney tissues were stained with HE and Yasue. The deposition and content of calcium oxalate crystals were observed under a light microscope.

The bacteria strain isolated from fresh feces of healthy adults was 100% as same as the known ATCC35274 bacteria strain, which means the strain screened is OxF. Among the 5 groups, there were no significant differences in body weight, Scr, BUN, serum calcium, blood magnesium, blood phosphorus, urinary magnesium and urinary phosphorus. The 24-hour urinary calcium excretion in the model group was significantly lower than that of the control group (P<0.05). After intervention with OxF solution, the 24-hour urinary calcium excretion in the 10⁸ CFU OxF group was significantly higher than that in the model group (P<0.05), while there was no significant difference between the other intervention groups and the model. The oxalic acid excretion of 10⁶ CFU OxF group and 10⁷ CFU OxF group was lower than that of the model, but the difference did not reach statistical significance (P>0.05). The 24 h oxalic acid excretion in the 10⁸ CFU OxF group was significantly lower than that of the model at the end of first week (P<0.05), and continued to decrease for the next 3 weeks. After 4 weeks of intervention, no crystal formation was observed in the control group under the deflection microscope, but a large amount of calcium oxalate crystals were formed in the renal cortex and renal medulla. The crystals were piled up and connected to each other. Yasue staining coincided with the calcium oxalate crystal in the same part of the kidneys. Compared with the model, there was no significant change in the score of calcium oxalate crystal in the kidneys of 10⁶ CFU OxF group and 10⁷ CFU OxF group, while the score of calcium oxalate crystal in the kidneys of 10⁸ CFU OxF group was significantly lower (P<0.05).

OxF are successively screened from healthy adults. Daily administration of 10⁸ CFU OxF can safely and effectively reduce the urinary oxalic acid excretion, prevent the formation of calcium oxalate crystals and inhibit the formation of stones in kidneys of rats.

Oxalobacter formigenes; Kidney calculi; Calcium oxalate