Response of germ-free mice to colonization with O. formigenes and altered Schaedler flora.

Colonization with Oxalobacter formigenes may reduce the risk of calcium oxalate kidney stone disease. To improve our limited understanding of host/O.formigenes and microbe/O.formigenes interactions, germ-free or altered Schaedler flora (ASF) mice were colonized with O.formigenes Germ-free mice were stably colonized with O.formigenes suggesting O.formigenes does not require other organisms to sustain its survival. Examination of intestinal material indicated no viable O.formigenes in the small intestine, ∼4 × 106 O.formigenes per 100mg contents in the cecum and proximal colon, and ∼0.02% of total cecal O. formigenes cells were tightly associated to the mucosa. O.formigenes did not alter the overall microbial composition of ASF, and ASF did not impact O.formigenes capacity to degrade dietary oxalate in the cecum. 24-hour urine and fecal collections within metabolic cages in semi-rigid isolators demonstrated that introduction of ASF into germ-free mice significantly reduced urinary oxalate excretion. These experiments also showed that mono-colonized O.formigenes mice excrete significantly more urinary calcium compared to germ-free mice, which may be due to degradation of calcium oxalate crystals by O.formigenes and the subsequent intestinal absorption of free calcium. In conclusion, the successful establishment of defined-flora O.formigenes mouse models should improve our understanding of O.formigenes host and microbe interactions. These data support the use of O.formigenes as a probiotic that has limited impact on the composition of the resident microbiota but providing efficient oxalate degrading function. IMPORTANCE: Despite evidence suggesting a lack of O. formigenes colonization is a risk factor for calcium oxalate stone formation, little is known about O. formigenes biology. This study is the first to utilize germ-free mice to examine the response to mono-colonization with O. formigenes and the impact of a defined bacterial cocktail, altered Schaedler flora, on O. formigenes colonization. This study demonstrates that germ-free mice on their regular diet remain mono-colonized with O. formigenes, and suggests that further studies with O. formigenes gnotobiotic mouse models could improve our understanding of O. formigenes biology and host/O. formigenes and microbe/O. formigenes interactions.