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Abstract: SA-PO281

Oxalate Degradation Rates of Oxalobacter formigenes

Session Information

Category: Bone and Mineral Metabolism

  • 402 Bone and Mineral Metabolism: Clinical

Authors

  • Ho, Melody, New York University, New York, New York, United States
  • Liu, Menghan, New York University School of Medicine, New York, New York, United States
  • Daniel, Steven L., Eastern Illinois University, Charleston, Illinois, United States
  • Goldfarb, David S., New York Harbor VAMC, New York, New York, United States
  • Nazzal, Lama, New York University School of Medicine, New York, New York, United States
Background

Kidney stones commonly affect US adults. In recent years, there has been increasing interest in the human anaerobic colonic bacterium Oxalobacter formigenes because of its ability to metabolize oxalate, and its potential to protect against calcium oxalate kidney stones. Currently, there are two known groups of O. formigenes (Group 1 and Group 2) with only a few isolates from each group characterized. In our experiments, we aimed to isolate O. formigenes from subjects with primary hyperoxaluria (PH), enteric hyperoxaluria (EH) and healthy controls (HC) to compare their metabolic activities. Understanding these differences will help expand our knowledge about this important organism and its effect on oxalate homeostasis in humans.

Methods

We collected fecal samples from 37 patients via clinical trials at New York University Langone Medical Center and Mayo Clinic with PH, EH and HC. We cultured fecal samples in 25mM oxalate-rich selective media, then isolated O. formigenes by picking characteristic colonies from calcium oxalate agar. We identified and grouped isolates using PCR and Sanger sequencing of the oxc gene. We then tested their oxalate consumption via Oxalate Degradation Assay to compute mean oxalate degradation rates (ODR) for each group of isolates.

Results

We isolated 25 O. formigenes colonies from 14 subjects, with all isolates belonging to either HC (n=11) or PH (n= 14) patients, and none from EH patients. Based on oxc sequences, we identified Group 1 (n=17) and Group 2 (n=5) strains, and potentially a new taxonomic group Group 3 (n=3). We were able to regrow 13 (76%) of 17, 1 (20%) of 5, and 1 (33%) of 3 Group 1, 2, and 3 strains, respectively. All 14 PH patient colonies were identified as Group 1, while HC had a mix of all three groups. Mean ODR was significantly higher in Group 1 vs Group 2 isolates (8.5 ± 3.3 vs 2.8 ± 1.9 micromole/hour, p=0.02). Group 3 isolates had intermediate ODR (5.7 ± 3.1) values. As expected, the ODRs of our Group 1 isolates were similar to the control group 1 strain OXCC13 ( 11.1 ± 1.2). Mean ODR between PH, EH and HC did not differ significantly.

Conclusion

We were able to isolate and characterize 25 colonies of O. formigenes, including a potential new group of O. formigenes. Group 1 strains appear to be most metabolically active in vitro, and were exclusively present in PH patients.

Funding

  • Private Foundation Support