Oxalobacter formigenes Colonization and Oxalate Dynamics in a Mouse Model

Abstract

Animal and human studies have provided compelling evidence that colonization of the intestine with Oxalobacter formigenes reduces urinary oxalate excretion and lowers the risk of forming calcium oxalate kidney stones. The mechanism providing protection appears to be related to the unique ability of O. formigenes to rely on oxalate as a major source of carbon and energy for growth. However, much is not known about the factors that influence colonization and host-bacterium interactions. We have colonized mice with O. formigenes OxCC13 and systematically investigated the impacts of diets with different levels of calcium and oxalate on O. formigenes intestinal densities and urinary and intestinal oxalate levels. Measurement of intestinal oxalate levels in mice colonized or not colonized with O. formigenes demonstrated the highly efficient degradation of soluble oxalate by O. formigenes relative to other microbiota. The ratio of calcium to oxalate in diets was important in determining colonization densities and conditions where urinary oxalate and fecal oxalate excretion were modified, and the results were consistent with those from studies we have performed with colonized and noncolonized humans. The use of low-oxalate purified diets showed that 80% of animals retained O. formigenes colonization after a 1-week dietary oxalate deprivation. Animals not colonized with O. formigenes excreted two times more oxalate in feces than they had ingested. This nondietary source of oxalate may play an important role in the survival of O. formigenes during periods of dietary oxalate deprivation. These studies suggest that the mouse will be a useful model to further characterize interactions between O. formigenes and the host and factors that impact colonization. Oxalobacter formigenes is a Gram-negative, obligate anaerobic bacterium that requires oxalate as a carbon source for energy and growth (1). O. formigenes is part of the microbiota in the large intestine of many humans and other mammalian species (1-6). A review of colonization frequencies conducted worldwide indicated that 38% to 77% of a normal population is colonized with O. formigenes (7). Recent evidence suggests that a lack of colonization with this oxalate-degrading specialist is a risk factor for idiopathic recurrent calcium oxalate kidney stone disease (8,9). Controlled diet studies in healthy human subjects have also indicated that O. formigenes-colonized individuals excrete significantly less oxalate in 24-hour urine collections when they consume diets containing moderate oxalate (250 mg) and low calcium (400 mg) levels (10).Little is known about how and when individuals become colonized or how O. formigenes persists over time. Studies to date suggest it occurs early in childhood (11), and if animal experiments provide any insight, it is obtained from the environment, not directly from the mother (12). Several studies have indicated that the intake of antibiotics can result in the loss of colonization (7,(13)(14)(15), and this is supported by decreased prevalence...

Response of Germfree Mice to Colonization by Oxalobacter formigenes and Altered Schaedler Flora

“…Colonization of GF or ASF mice with O. formigenes did not result in significant reductions in urinary oxalate excretion. This finding is consistent with our previous study, which showed that urinary oxalate excretion did not decrease with O. formigenes colonization when conventional mice were fed a diet similar to that used in this study (i.e., high calcium and normal oxalate levels) (11). In comparison, ASF or ASF/OxF colonization of GF mice resulted in ϳ40% reductions in urinary oxalate excretion.…”

“…formigenes interactions. We showed previously, with conventional mice, that the ratio of calcium to oxalate in the diet was important in determining colonization densities and conditions under which urinary oxalate excretion and fecal oxalate excretion were modified (11), and findings were consistent with studies we performed with naturally colonized and noncolonized human subjects (21). In the present study, we utilized GF mice to examine O. formigenes-altered Schaedler flora interactions and the response to monocolonization with O. formigenes.…”

“…Animals had free access to food (LM-485 autoclavable rodent diet; Teklad, Madison, WI) and water. Diet LM-485 contains 10 mg calcium/g diet and 1 mg oxalate/g diet and is considered a high-calcium/normal-oxalate rodent chow diet, similar to that used in our previous study (11). Homogenization of the diet in water versus 2 M hydrochloric acid was used to determine how much of the oxalate was incorporated in crystals; homogenization in acid ensures complete dissolution of all crystalline oxalate.…”

“…Colonization has been demonstrated to induce gastrointestinal oxalate secretion, which may be an important mechanism by which this organism decreases oxalate levels within the body (10,13,14). Our recent studies with conventional mice artificially colonized with O. formigenes indicated that nondietary sources of oxalate, such as enteric oxalate secretion, may play an important role in the survival of O. formigenes during periods of dietary oxalate deprivation (11). Monocolonization and defined-flora models have become useful tools for the study of both microbe-microbe and host-bacterium interactions (15).…”

“…Rodent models colonized with O. formigenes have been used to answer a number of biological questions (9)(10)(11)(12). Colonization has been demonstrated to induce gastrointestinal oxalate secretion, which may be an important mechanism by which this organism decreases oxalate levels within the body (10,13,14).…”