Hyperoxaluria is a condition of excessive urinary oxalate secretion, a condition frequently associated with kidney stones. The human diet contains a considerable quantity of oxalate and plays a significant role in raising urinary oxalate levels( Reference Holmes, Goodman and Assimos 1 ). Moreover, probiotic treatment has been reported as a successful strategy for lowering urinary oxalate( Reference Campieri, Campieri and Bertuzzi 2 ). Oxalobacter formigenes is an anaerobic intestinal bacterium with the ability to break down oxalate, thus may impact on hyperoxaluria( Reference Mittal and Kumar 3 ). Thus the aim of present study was to assess the oxalate status after inoculation of O. formigenes. In the current study, faecal microbial fermentation was carried out by the use of an in vitro batch culture system along with test foods (wheat bran)( Reference Olano-Martin, Gibson and Rastall 4 ). Pure oxalate salt was used as a control substrate. Analysis of organic acids, oxalate and formate, was performed using a method described by Savage et al. and Ehrlich( Reference Savage, Vanhanen and Mason 5 , Reference Ehrlich 6 ). Samples were collected for subsequent analysis at 0 min, 2, 4, 8 and 24 h. ANOVA analysis with Tukey HSD test was used to assess the significant differences.
Oxalate levels decreased after addition of O. formigenes whilst food was being fermented. However, a continuous increase in oxalate was observed under the same conditions without the O. formigenes addition (Fig. 1 and 2; P < 0.05). Reduction of oxalate in the test food sample was due to increased levels of soluble oxalate that has been reported to be approximately 30% of the total oxalate( Reference Israr, Frazier and Gordon 7 ) enabling O. formigenes to work efficiently following fermentation of wheat bran and in the presence of oxalate salt. In conclusion, O. formigenes was observed to reduce oxalate levels in an in vitro colonic batch system, suggesting that there is a potential for this microorganism to reduce hyperoxaluria in vivo. Therefore the probiotic O. formigenes, may be an effective strategy to reduce plasma oxalates in those who have suffered kidney stones, although this requires testing in a randomly controlled human study for confirmation.