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Aim: To examine whether enhanced diversity or numbers of oxalate-degrading bacteria in the gastrointestinal tracts of black South Africans play a role in determining the rarity of urolithiasis in this group. Methods and Results: Fresh faecal samples collected from healthy black and white South African male volunteers were analysed in terms of bacterial oxalate-degrading activity, bacterial diversity and relative species abundance. Varied bacterial populations prepared from samples from the low-risk black group showed a significantly higher level of oxalate degradation. Denaturing gradient gel electrophoresis analyses of Lactobacillus and related spp. and Bifidobacterium spp. 16S rRNA PCR products revealed a significantly higher faecal Lactobacillus diversity for the low-risk black group relative to the higherrisk white group. Quantitative real-time PCR experiments did not show any significant differences between the study groups for Lactobacillus and related spp.. However, Bifidobacterium spp. were present at a significantly higher relative abundance in the black group. Oxalobacter formigenes was present only at very low levels in either group. Conclusions: The low abundance of O. formigenes and increased diversity and abundance of oxalate-degrading Lactobacillus and Bifidobacterium spp. in the black South African population suggest that these strains rather than O. formigenes may protect this group against calcium oxalate kidney stone disease. Significance and Impact of the Study: The South African black population harbours a pool of potential oxalate-degrading lactic acid bacteria, which is more abundant and diverse than that of white South Africans. This may be useful in developing probiotics for calcium oxalate kidney stone prophylaxis.

To our knowledge increased citraturia has not been previously reported for any essential fatty acid. We hypothesize that evening primrose oil inhibits lipogenesis, thereby decreasing citrate consumption. For the decrease in oxaluria we suggest that evening primrose oil alters membrane fatty acid composition, thereby inhibiting the modulation of protein kinases that lead to hyperoxaluria. In regard to decreased calciuria we suggest that evening primrose oil modulates delta-5 and/or delta-6-desaturase, thereby inhibiting the production of arachidonic acid and prostaglandin E2, which influence calciuria. The different response in the 2 groups with respect to oxaluria confirms previously reported differences in sensitivity toward supplemental ingestion. Data suggest that evening primrose oil supplementation should be investigated as a possible conservative treatment for calcium oxalate urolithiasis.

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