Oxalobacter Formigenes Colonization and Oxalate Excretion in Healthy Adults
Phase: NA
Conditions: Calcium Oxalate Urolithiasis
Sponsor: University of Alabama at Birmingham

 
Official Title: Oxalobacter Formigenes Colonization and Oxalate Excretion in Healthy Adults 
NCT#: 03752684 
Document Date: May 22, 2025 
 
 
 
 
 
 

STUDY PROTOCOL 
 
Objective of the study 
 
The primary objective of the study was to determine if healthy adults can be colonized with Oxalobacter 
formigenes, a naturally occurring oxalate degrading intestinal bacterium, and if colonization results in a decrease 
in urinary oxalate excretion on a fixed diet. 
 
Study Design 
 
This study was designed as a sequential, diet-controlled study. The study recruited healthy adults from the 
Greater Birmingham area. The individuals were recruited, consented, and had blood samples collected at the 
UAB CCTS Clinical Research Unit. Sample processing, data acquisition and analysis was performed in the 
Urology Stone Research Laboratory.  
 
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Inclusion criteria: not colonized with Oxalobacter formigenes, mentally competent adults without history 
of kidney stones, who are able to read and comprehend the consent form (written in English); >18 and 
<65 yrs; BMI 18.5-40 kg/m2; good health as judged from a medical history without other medical 
comorbidities. individuals will need a normal blood comprehensive metabolic panel.  
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Exclusion criteria: colonized with Oxalobacter formigenes, history of any hepatic, renal (including kidney 
stone disease), bowel or endocrine disease (including diabetes) or any other condition that may influence 
the absorption, transport or urine excretion of ions, which will compromise the interpretation of results; 
abnormal blood metabolic profiles; poor 24 hour urine collections judged by 24 hour urine creatinine 
excretion (indicative of not collecting all urine in 24 hour period); pregnancy, intention to become pregnant 
in the near future, or lactation; <18 and > 65 years of age; BMI<18.5 >40 kg/m2 
 
Study Methods 
 
Screening. The screening phase involved a fasted blood draw for comprehensive metabolic profile (CMP), two 24-
hr urine collections (creatinine) and stool collections on self-choice diets. Screening blood tests were used as a 
health assessment, and urinary creatinine as measure of the candidates’ ability to accurately collect urine. Stool at 
screening was used to test for O. formigenes colonization. If negative, participants were further tested after 
consuming a high oxalate containing meal.  
 
Pre-Colonization Fixed Diet Study: Participants who passed screening collected stool and 24-hour urine 
specimens while ingesting a moderately high oxalate (210 – 240 mg/day) and low calcium (500 - 700 mg 
calcium/day) diet. For reference, a healthy diet rich in whole grain products, fruits and vegetables may contain 
close to 200 mg of oxalate per day, and the recommended dietary calcium intake per day for calcium oxalate 
kidney stone formers is 1000 mg. Twenty-four-hour urine and stool specimens were collected on days 3-5 of 
each dietary phase to allow for dietary equilibration. Lack of colonization with O. formigenes (pre-colonization 
phase) was again confirmed by stool culture.  
 
Oxalobacter formigenes colonization procedure: Following completion of the pre-colonization controlled diet, 
participants ingested live O.formigenes,cells spread on a sandwich. One week later participants collected stool 
for colonization culture testing.  
 
Post-Colonization Fixed Diet Study: Successfully colonized participants repeated stool and urine collections on 
the same controlled diet.  
 
Assays: Urine and stool oxalate was measured in urines and stool by ion chromatography coupled with mass 
spectrometry. 
 
 
 
 

Statistical Analysis Plan 
The primary outcome measure was decrease in urinary oxalate content after colonization with O. formigenes on 
the fixed diet. The secondary outcome was decrease in stool oxalate content after colonization with O. 
formigenes on the fixed diet.  
The means of oxalate content of repeated urine and stool collections for each phase (pre and post colonization) 
were used, and the decrease in oxalate content after colonization determined for each participant. Paired 
comparisons were performed using linear mixed-effects models (for repeated measures). The covariates 
included gender, body mass index, age, and a dichotomous variable denoting loss of colonization during the 
follow-up period (adjusted analyses); these covariates were included because of potential associations with 
endogenous oxalate synthesis or gut permeability and absorption. Statistical tests were two-sided and were 
performed using a significance level of 5%. Statistical analyses were performed using SAS software (version 
9.4; SAS Institute, Cary, NC). PROC MIXED of SAS was used to perform linear mixed effects models analyses. 
The sample size was selected based on feasibility considerations for this pilot Basic Experimental Study in 
Humans (BESH).