Oxalobacter formigenes is a Gram negative oxalate-degrading anaerobic bacterium that was first isolated from the gastrointestinal tract of a sheep in 1985.

[1] To date, the bacterium has been found to colonize the large intestines of numerous vertebrates, including humans, and has even been isolated from freshwater sediment.

[9][11] Based on fatty acid profile, 16S ribosomal RNA sequencing, and DNA probes specific to the oxc (oxalyl-CoA decarboxylase) gene and frc (formyl-CoA transferase), O. formigenes has been divided into two groups.

While oxalate is the main carbon source, small amounts of acetate and yeast extract are supportive of growth.

Instead, bacteria are cultured in the presence of antibiotics and screened for viability using opaque anaerobic oxalate agar.

[2][20][21] This method demonstrated that O. formigenes is resistant to nalidixic acid, ampicillin, amoxicillin, streptomycin, and vancomycin.

[20][21] O. formigenes was also found to be susceptible to ciprofloxacin, clarithromycin, clindamycin, doxycycline, gentamicin, levofloxacin, metronidazole, and tetracycline.

[2] However, by slowly acclimatizing sheep to high-oxalate intake, they would survive the consumption of large quantities of oxalate-rich plants.

[30] This led to the proposal that resident oxalate-degrading bacteria were enriched by the gradual introduction to a oxalate-rich diet, which protected the sheep from oxalate-induced renal damage.

[33] Initial research pointed to the loss of oxalate-degrading bacteria, such as O. formigenes, following antibiotic usage as primary contributor to calcium oxalate kidney stone disease.

[34][35] Colonization with O. formigenes has been observed to results in a decrease in urinary oxalate[35][4] and reduced frequency of kidney stones[4][7][36] Recent work using next-generation sequencing has found that O. formigenes colonizes both calcium oxalate kidney stone formers and non-stone forming controls.