Molecular identification of Oxalobacter formigenes with the polymerase chain reaction in fresh or frozen fecal samples

The role of microbiome: a novel insight into urolithiasis

Urolithiasis, referred to as the formation of stones in the urinary tract, is a common disease with growing prevalence and high recurrence rate worldwide. Although researchers have endeavoured to explore the mechanism of urinary stone formation for novel effective therapeutic and preventative measures, the exact aetiology and pathogenesis remain unclear. Propelled by sequencing technologies and culturomics, great advances have been made in understanding the pivotal contribution of the human microbiome to urolithiasis. Indeed, there are diverse and abundant microbes interacting with the host in the urinary tract, overturning the dogma that urinary system, and urine are sterile. The urinary microbiome of stone formers was clearly distinct from healthy individuals. Besides, dysbiosis of the intestinal microbiome appears to be involved in stone formation through the gut-kidney axis. Thus, the human microbiome has potential significant implications for the aetiology of urolithiasis, providing a novel insight into diagnostic, therapeutic, and prognostic strategies. Herein, we review and summarize the landmark microbiome studies in urolithiasis and identify therapeutic implications, challenges, and future perspectives in this rapidly evolving field. To conclude, a new front has opened with the evidence for a microbial role in stone formation, offering potential applications in the prevention, and treatment of urolithiasis.

Probiotics in the Prevention of the Calcium Oxalate Urolithiasis

Nephrolithiasis ranks third among urological diseases in terms of prevalence, making up about 15% of cases. The continued increase in the incidence of nephrolithiasis is most probably due to changes in eating habits (high protein, sodium, and sugar diets) and lifestyle (reduced physical activity) in all developed countries. Some 80% of all kidney stones cases are oxalate urolithiasis, which is also characterized by the highest risk of recurrence. Frequent relapses of nephrolithiasis contribute to severe complications and high treatment costs. Unfortunately, there is no known effective way to prevent urolithiasis at present. In cases of diet-related urolithiasis, dietary changes may prevent recurrence. However, in some patients, the condition is unrelated to diet; in such cases, there is evidence to support the use of stone-related medications. Interestingly, a growing body of evidence indicates the potential of the microbiome to reduce the risk of developing renal colic. Previous studies have primarily focused on the use of Oxalobacterformigenes in patients with urolithiasis. Unfortunately, this bacterium is not an ideal probiotic due to its antibiotic sensitivity and low pH. Therefore, subsequent studies sought to find bacteria which are capable of oxalate degradation, focusing on well-known probiotics including Lactobacillus and Bifidobacterium strains, Eubacterium lentum, Enterococcus faecalis, and Escherichia coli.

Current update and future directions on gut microbiome and nephrolithiasis

The incidence of nephrolithiasis is increasing worldwide. Understanding how gut microbiome influences oxalate homeostasis has the potential to offer new strategies to prevent nephrolithiasis. The literature was reviewed to gather the evidence on the association between gut microbiome, hyperoxaluria and nephrolithiasis, and to identify the therapeutic interventions focused on the gut microbiome that could decrease hyperoxaluria and prevent nephrolithiasis. Gut microbiome is constituted by a plethora of microbiota including Oxalobacter formigenes (Oxf) and lactobacilli. Oxf can degrade dietary oxalate and induce enteral oxalate secretion. Animal studies suggested an association between oral Oxf supplementation and a decrease in hyperoxaluria. However, human studies have showed inconsistent results. Oral supplementation of lactobacilli did not show benefit in decreasing the hyperoxaluria. Antibiotic exposure, by affecting the gut microbiome, has been associated with an increase in nephrolithiasis. In vivo studies suggest fecal transplantation as a potential treatment option for reducing nephrolithiasis, but needs further evaluation in clinical studies. The current evidence suggests an association between gut microbiome and nephrolithiasis. However, the strategies focused on modulating gut microbiome for decreasing hyperoxaluria and preventing nephrolithiasis need further research. Judicious use of antibiotics in those predisposed to nephrolithiasis offers a preventative strategy for decreasing nephrolithiasis.

Oxalobacter formigenes reduce the risk of kidney stones in patients exposed to oral antibiotics: a case-control study

This is the first prospective study to investigate the association between kidney stones, bone mineral density, serum testosterone, colon cancer and O. formigenes colonization. 40 kidney stone patients and 85 controls were enrolled. O. formigenes colonization was established. BMD was examined from T- and Z-scores using dual energy absorptiometry. O. formigenes was found in 28 of 40 cases and 80 of 85 controls. BMD was significantly reduced in patients (p < 0.05). The evaluation revealed a significant association between lowered O. formigenes colonization and low testosterone. Urinary calcium and oxalates levels were greater in patient. Serum testosterone and urinary citrate concentrations was reduced in patients with a significant difference. Also an association between O. formigenes and colon cancer was noted. Absence of O. formigenes might stand for a pathogenic factor in calcium oxalate stone, low bone mineral density, low testosterone levels and also colon cancer, when antibiotics are prescribed generously.

Simultaneous use of oxalate-degrading bacteria and herbal extract to reduce the urinary oxalate in a rat model: A new strategy

Objective:

Urinary stones with oxalate composition can cause kidney failure. Recent findings evidenced that probiotics are effective in reducing oxalate absorption in these subjects based on their high colonic absorption levels at baseline. The purpose of this study was to evaluate the effect of the simultaneous use of oxalate-degrading bacteria, Urtica dioica and T. terrestris extract in reducing urinary oxalate.

Materials and Methods:

Anti-urolithiatic activity of Urtica dioica and T. terrestris extract and probiotic by using ethylene glycol induced rat model. In this study, 4 strains of Lactobacillus and 2 strains of Bifidobacterium and also 2 strains of L. paracasei (that showed high power in oxalate degrading in culture media) were used. Male Wistar rats were divided into four groups (n=6). The rats of group-I received normal diet (positive control group) and groups-II (negative control group), III, IV rats received diet containing ethylene glycol (3%) for 30 days. Groups III rats received Urtica dioica and T. terrestris extract. Groups IV rats received extracts + probiotic for 30 days.

Findings:

The results show that the use of herbal extracts (Urtica dioica and T. terrestris) reduced the level of urinary oxalate and other parameters of urine and serum. Also, the accumulation of calcium oxalate crystals in the kidney tissue was significantly reduced.

Conclusion:

Considering that the formation of calcium oxalate crystals can cause inflammation and tissue damage in the kidney, the use of herbal extracts with oxalate degrading bacteria can be a new therapeutic approach to preventing the formation of kidney stones.

Defining Dysbiosis in Patients with Urolithiasis

The prevalence of urinary stone disease (USD) is rapidly rising. However, the factors driving this increase are unknown. Recent microbiome studies suggest that dysbiosis may in part contribute to the increasing prevalence. The objective of the current study was to determine the nature and location of dysbiosis associated with USD. We conducted microbiome analysis from the gastrointestinal and urinary tracts, along with a metabolomic analysis of the urinary metabolome, from subjects with an active episode of USD or no history of the disease. Higher rates of antibiotic use among USD patients along with integrated microbiome and metabolomic results support the hypothesis that USD is associated with an antibiotic-driven shift in the microbiome from one that protects against USD to one that promotes the disease. Specifically, our study implicates urinary tract Lactobacillus and Enterobacteriaceae in protective and pathogenic roles for USD, respectively, which conventional, culture-based methods of bacterial analysis from urine and kidney stones would not necessarily detect. Results suggest that antibiotics produce a long-term shift in the microbiome that may increase the risk for USD, with the urinary tract microbiome holding more relevance for USD than the gut microbiome.

Inhibition of urinary stone disease by a multi-species bacterial network ensures healthy oxalate homeostasis

The incidence of urinary stone disease is rapidly increasing, with oxalate being a primary constituent of approximately 80% of all kidney stones. Despite the high dietary exposure to oxalate by many individuals and its potential nephrotoxicity, mammals do not produce enzymes to metabolize this compound, instead relying in part on bacteria within the gut to reduce oxalate absorption and urinary excretion. While considerable research has focused on isolated species of oxalate-degrading bacteria, particularly those with an absolute requirement for oxalate, recent studies have pointed to broader roles for microbiota both in oxalate metabolism and inhibition of urinary stone disease. Here we examined gut microbiota from patients with and live-in individuals without urinary stone disease to determine if healthy individuals harbored a more extensive microbial network associated with oxalate metabolism. We found a gender-specific association between the gut microbiota composition and urinary stone disease. Bacteria enriched in healthy individuals largely overlapped with those that exhibited a significant, positive correlation with Oxalobacter formigenes, a species presumed to be at the center of an oxalate-metabolizing microbial network. Furthermore, differential abundance analyses identified multiple taxa known to also be stimulated by oxalate in rodent models. Interestingly, the presence of these taxa distinguished patients from healthy individuals better than either the relative abundance or colonization of O. formigenes. Thus, our work shows that bacteria stimulated by the presence of oxalate in rodents may, in addition to obligate oxalate users, play a role in the inhibition of urinary stone disease in man.

Comparative prevalence of Oxalobacter formigenes in three human populations

There has been increasing interest in the human anaerobic colonic bacterium Oxalobacter formigenes because of its ability to metabolize oxalate, and its potential contribution to protection from calcium oxalate kidney stones. Prior studies examining the prevalence of this organism have focused on subjects in developed countries and on adults. Now using O. formigenes-specific PCR, we have compared the prevalence of these organisms among subjects in two remote areas in which modern medical practices have hardly been present with a USA group of mothers and their infants for the first three years of life. Among the Amerindians of the Yanomami-Sanema and Yekwana ethnic groups in Venezuela and the Hadza in Tanzania, O. formigenes was detected in 60–80% of the adult subjects, higher than found in adults from USA in this and prior studies. In young children, the prevalence was much lower in USA than in either tribal village. These data extend our understanding of the epidemiology of O. formigenes carriage, and are consistent with the hypothesis that the rising incidence of kidney stones is associated with the progressive loss of O. formigenes colonization in populations that have been highly impacted by modern medical practices.

Calcium Oxalate Urolithiasis: A Case of Missing Microbes?

INTRODUCTION

Urinary stone disease (USD) has known associations with the gut microbiota. Approximately 80% of kidney stones contain oxalate as a primary constituent and diverse oxalate-degrading bacteria exist within the human gut, which may protect against USD. Although bacteriotherapy represents a promising strategy to eliminate oxalate and reduce the risk of USD, oxalate-degrading probiotics have had limited success. To identify limitations of oxalate-degrading probiotics and refine development of bacteriotherapies to prevent USD, we review the literature associated with the gut microbiota and USD.

MATERIALS AND METHODS

A literature search was performed to identify publications that examine the role of oxalate-degrading bacteria or the whole gut microbiota in oxalate metabolism and the pathophysiology of USD. We conducted a meta-analysis of studies that examined the association of the whole gut microbiota with USD. In addition, we evaluated the gut microbiota of healthy individuals and those with comorbidities related to USD using publically available data from the American Gut Project (AGP).

RESULTS

Studies on Oxalobacter formigenes reveal that colonization by this species is not a good predictor of USD risk or urinary oxalate excretion. The species of oxalate-degrading bacteria used in probiotics and duration of administration do not impact efficacy or persistence. Studies focused on the whole gut microbiota reveal broad shifts in the gut microbiota associated with USD and a diverse microbial network is associated with oxalate metabolism. AGP data analysis demonstrated a strong overlap in microbial genera depleted in diseased individuals among USD and comorbidities.

CONCLUSIONS

The associations between the gut microbiota and USD extend beyond individual functional microbial species. Common shifts in the gut microbiota may facilitate the onset of USD and/or comorbidities. The successful development of bacteriotherapies to inhibit USD will need to incorporate strategies that target a broad diversity of bacteria rather than focus on a few specialist species.

Primary and secondary hyperoxaluria: Understanding the enigma

Hyperoxaluria is characterized by an increased urinary excretion of oxalate. Primary and secondary hyperoxaluria are two distinct clinical expressions of hyperoxaluria. Primary hyperoxaluria is an inherited error of metabolism due to defective enzyme activity. In contrast, secondary hyperoxaluria is caused by increased dietary ingestion of oxalate, precursors of oxalate or alteration in intestinal microflora. The disease spectrum extends from recurrent kidney stones, nephrocalcinosis and urinary tract infections to chronic kidney disease and end stage renal disease. When calcium oxalate burden exceeds the renal excretory ability, calcium oxalate starts to deposit in various organ systems in a process called systemic oxalosis. Increased urinary oxalate levels help to make the diagnosis while plasma oxalate levels are likely to be more accurate when patients develop chronic kidney disease. Definitive diagnosis of primary hyperoxaluria is achieved by genetic studies and if genetic studies prove inconclusive, liver biopsy is undertaken to establish diagnosis. Diagnostic clues pointing towards secondary hyperoxaluria are a supportive dietary history and tests to detect increased intestinal absorption of oxalate. Conservative treatment for both types of hyperoxaluria includes vigorous hydration and crystallization inhibitors to decrease calcium oxalate precipitation. Pyridoxine is also found to be helpful in approximately 30% patients with primary hyperoxaluria type 1. Liver-kidney and isolated kidney transplantation are the treatment of choice in primary hyperoxaluria type 1 and type 2 respectively. Data is scarce on role of transplantation in primary hyperoxaluria type 3 where there are no reports of end stage renal disease so far. There are ongoing investigations into newer modalities of diagnosis and treatment of hyperoxaluria. Clinical differentiation between primary and secondary hyperoxaluria and further between the types of primary hyperoxaluria is very important because of implications in treatment and diagnosis. Hyperoxaluria continues to be a challenging disease and a high index of clinical suspicion is often the first step on the path to accurate diagnosis and management.

Oxalobacter colonization in the morbidly obese and correlation with urinary stone risk

OBJECTIVE

To establish the baseline preoperative prevalence of Oxalobacter formigenes (OF) colonization in a cohort of obese patients scheduled for Roux-en-Y gastric bypass (RYGB) and determine the effect of OF colonization on urinary oxalate excretion. It has been proposed that loss of OF colonization after RYGB may contribute to the development of hyperoxaluria.

METHODS

Adult patients scheduled to undergo RYGB were requested to provide a stool specimen and 24-hour urine collection before surgery. OF colonization status was determined by the calcium precipitation test. The 24-hour urine specimens were analyzed by the Litholink Corporation (Chicago, IL).

RESULTS

Of the 51 patients submitting initial stool specimens, only 8 (16%) tested positive for OF, whereas 43 (84%) were negative. Patients colonized with OF were older than uncolonized subjects (52.9±6.8 vs 46.0±10.4 years, P=.03). Urinary oxalate was not significantly different between these groups (P=.14).

CONCLUSION

OF colonization is uncommon in morbidly obese patients (16%) before surgery. Because hyperoxaluria develops in more than 50% of patients after RYGB, it is unlikely that loss of OF colonization is the primary cause.

Factors related to colonization with Oxalobacter formigenes in U.S. adults

GOALS

To elucidate the determinants of Oxalobacter formigenes colonization in humans.

BACKGROUND

O. formigenes is a gram-negative anaerobic bacterium that colonizes the colon of a substantial proportion of the normal population and metabolizes dietary and endogenous oxalate. The bacterium has been associated with a large reduction in the odds of recurrent calcium oxalate kidney stones. Subjects were 240 healthy individuals from Massachusetts and North Carolina. O. formigenes was detected by culture of fecal swabs. Information on factors of interest was obtained by telephone interviews and self-administered questionnaires.

STUDY RESULTS

The overall prevalence of O. formigenes was 38%. Use of specific antibiotics previously thought to affect the bacterium was significantly related to colonization, with prevalences of 17%, 27%, and 36%, for those who had used these drugs <1, 1-5, and >5 years ago, compared with 55% in nonusers. There were no significant associations with demographic factors, nutrient intake, or medical history, although the prevalence appeared to increase somewhat with increasing oxalate consumption.

CONCLUSIONS

Some antibiotics markedly affect colonization with O. formigenes. Although no other factor was identified as having a material influence on the prevalence of the bacterium, there is much to learn about how an individual acquires the organism and which factors affect persistence of colonization.

Intestinal colonization with Oxalobacter formigenes and its relation to urinary oxalate excretion in pediatric patients with idiopathic calcium urolithiasis

BACKGROUND AND AIM

Oxalobacter formigenes is an intestinal bacterium that utilizes oxalate as the only source of energy. It has been suggested that the lack of colonization with this organism may be a risk factor for calcium oxalate urolithiasis. Because this problem was not investigated in pediatric stone formers, we decided to assess it in our patients.

METHODS

The presence of O. formigenes in stool samples of 76 children and adolescents (aged 4.1-18 years) with idiopathic calcium urolithiasis (36 with chemically confirmed calcium oxalate stones and 40 children with a strong clinical suspicion of this type of urolithiasis) was assessed using PCR method. Simultaneously, urinary oxalate excretion was measured in this group. Fifty healthy, age- and sex-matched subjects served as controls.

RESULTS

O. formigenes was found in 21/76 patients (27.6%). In controls, frequency of colonization was similar (26%). The median 24h urinary oxalate excretion in patients colonized with O. formigenes was significantly lower in comparison with non-colonized patients, 0.319 (range 0.141-0.546) and 0.437 (range 0.198-0.967) mmol/1.73 m(2)/24h, respectively.

CONCLUSIONS

Higher urinary oxalate excretion in children with calcium urolithiasis may be a result of the absence of O. formigenes. The reasons for similarly low intestinal colonization with this bacterium in normal subjects and stone formers remain speculative. Thus, further studies are necessary to clarify this issue.

Oxalobacter formigenes may reduce the risk of calcium oxalate kidney stones

Most kidney stones are composed primarily of calcium oxalate. Oxalobacter formigenes is a Gram-negative, anaerobic bacterium that metabolizes oxalate in the intestinal tract and is present in a large proportion of the normal adult population. It was hypothesized that the absence of O. formigenes could lead to increased colonic absorption of oxalate, and the subsequent increase in urinary oxalate could favor the development of stones. To test this hypothesis, a case-control study involving 247 adult patients with recurrent calcium oxalate stones and 259 age-, gender-, and region-matched control subjects was performed. The prevalence of O. formigenes, determined by stool culture, was 17% among case patients and 38% among control subjects; on the basis of multivariate analysis controlling demographic factors, dietary oxalate, and antibiotic use, the odds ratio for colonization was 0.3 (95% confidence interval 0.2 to 0.5). The inverse association was consistently present within strata of age, gender, race/ethnicity, region, and antibiotic use. Among the subset of participants who completed a 24-h urine collection, the risk for kidney stones was directly proportional to urinary oxalate, but when urinary factors were included in the multivariable model, the odds ratio for O. formigenes remained 0.3 (95% confidence interval 0.1 to 0.7). Surprisingly, median urinary oxalate excretion did not differ with the presence or absence of O. formigenes colonization. In conclusion, these results suggest that colonization with O. formigenes is associated with a 70% reduction in the risk for being a recurrent calcium oxalate stone former.

Oxalobacter formigenes: a potential tool for the treatment of primary hyperoxaluria type 1

Primary hyperoxaluria is characterized by severe urolithiasis, nephrocalcinosis, and early renal failure. As treatment options are scarce, we aimed for a new therapeutic tool using colonic degradation of endogenous oxalate by Oxalobactor formigenes. Oxalobacter was orally administered for 4 weeks as frozen paste (IxOC-2) or as enteric-coated capsules (IxOC-3). Nine patients (five with normal renal function, one after liver-kidney transplantation, and three with renal failure) completed the IxOC-2 study. Seven patients (six with normal renal function and one after liver-kidney transplantation) completed the IxOC-3 study. Urinary oxalate or plasma oxalate in renal failure was determined at baseline, weekly during treatment and for a 2-week follow-up. The patients who showed >20% reduction both at the end of weeks 3 and 4 were considered as responders. Under IxOC-2, three out of five patients with normal renal function showed a 22-48% reduction of urinary oxalate. In addition, two renal failure patients experienced a significant reduction in plasma oxalate and amelioration of clinical symptoms. Under IxOC-3 treatment, four out of six patients with normal renal function responded with a reduction of urinary oxalate ranging from 38.5 to 92%. Although all subjects under IxOC-2 and 4 patients under IxOC-3 showed detectable levels of O. formigenes in stool during treatment, fecal recovery dropped directly at follow up, indicating only transient gastrointestinal-tract colonization. The preliminary data indicate that O. formigenes is safe, leads to a significant reduction of either urinary or plasma oxalate, and is a potential new treatment option for primary hyperoxaluria.

Prevention of nephrolithiasis by Lactobacillus in stone-forming rats: a preliminary study

Hyperoxaluria is a risk factor for renal stones. It appears to be sustained by increased dietary load or increased intestinal absorption. The aim of this study was to evaluate whether oral administration of lactobacilli could prevent urolithiasis in stone-forming rats. Oxalate-degrading activities of lactobacilli were evaluated by measuring the oxalate level in a culture medium after inoculation with lactobacilli. Only the strains of Lactobacillus having oxalate-degrading activity were used. Sprague-Dawley rats were fed a powdered standard diet containing 3% sodium oxalate and/or received 100 mg/kg of celecoxib for the first 8 days by gavage, before or after the beginning of this experiment (groups with previous treatment or with co-treatment). Rats were sacrificed after 4 weeks and kidneys were harvested for the assay of crystal formation under a dissecting microscope. Twenty-four-hour urine collections were performed before kidney harvest. Only two strains, Lactobacillus casei HY2743 and L. casei HY7201 out of 31 strains of Lactobacillus were able to degrade oxalate. In both groups of co-treatment and previous treatment with L. casei HY2743 and L. casei HY7201, urine oxalate excretion decreased compared to the group without lactobacilli. The dissecting microscope examination of kidneys in the rats in two previous treatment groups and the co-treatment group with L. casei HY7201 showed less abundant crystals than control groups. Our results show that lactobacilli may be used as a potential therapeutic strategy in the prevention of urinary stones.

[Calcium oxalate stones and hyperoxaluria. What is certain? What is new?]

Approximately 4 million Germans suffer from stone disease. In the majority of cases (70-75%) it is calcium oxalate. Its pathophysiology is complex and comprises disorders such as hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria, and hypomagnesuria. These biochemical changes in urine are well known as "classic" risk factors of calcium oxalate stone formation. However, studies in the last decade showed that calcium oxalate stones are strongly related with other diseases or disorders such as overweight, hypertension, or a lack of oxalate-degrading bacteria in the gut. The evidence for these "new" risk factors in the literature is very strong. It is particularly important in regard to effective treatment and aftercare of patients with calcium oxalate stones to be familiar with both the "classic" and the new risk factors.

Gut-inhabiting bacterium Oxalobacter formigenes: role in calcium oxalate urolithiasis

Oxalate plays a crucial role in the formation of most renal stones. Oxalate is a common constituent of most diets and a byproduct of metabolism, and if it is not sufficiently degraded, it may accumulate. In humans, gut bacteria degrade 70 to 100 mg of oxalate per day. Oxalobacter formigenes is a gram-negative, obligately anaerobic, rod-shaped bacterium with an absolute requirement for oxalate. Although not present in the gut at birth, it quickly colonizes most children, and there is epidemiologic evidence that its absence is a risk factor in calcium oxalate stone formation. We review the metabolism, genetics, and identification of this organism and its possible therapeutic role in recurrent stone-forming patients.

Urinary oxalate levels and the enteric bacterium Oxalobacter formigenes in patients with calcium oxalate urolithiasis

OBJECTIVES

We performed a prospective study to evaluate the intestinal colonization of Oxalobacter formigenes and its relationship with urinary oxalate levels in patients with calcium oxalate stone disease.

METHODS

One hundred and three patients with calcium oxalate urolithiasis, ranging in age from 21 to 73 years (mean age, 47 years) who were followed from August 2000 to September 2001 participated in this study. Fresh stool and 24-hour urine samples were collected. Genus specific oligonucleotide sequences corresponding to the homologous regions residing in the oxc gene were designed. In order to quantify O. formigenes in clinical specimens, a quantitative-PCR-based assay system utilizing a competitive DNA template as an internal standard was developed. Urine volume, pH, creatinine, oxalate, calcium, magnesium, phosphate, citrate and uric acid were measured.

RESULTS

Intestinal Oxalobacteria were detected in 45.6% (n=47) of calcium oxalate stone patients by PCR. In stone formers who tested negative for Oxalobacteria, the average urinary oxalate level was 0.36 mmol/day, and this compared to 0.29 mmol/day for those patients that tested positive for Oxalobacteria (p<0.05). Mean colony forming units per gram of stool of all patients was 1.1 x 10(7) (0-4.1 x 10(8)), and the level of 24 hours urine oxalate significantly decreased with increasing level of colony forming units of O. formigenes (r=-0.356, p=0.021).

CONCLUSION

Our results support the concept that O. formigenes is important in maintaining oxalate homeostasis and that its absence from the gut may be the risk of calcium oxalate urolithiasis.

The association of nephrolithiasis with cystic fibrosis

BACKGROUND

There is a growing body of evidence regarding the association between cystic fibrosis (CF) and nephrolithiasis and the role that Oxalobacter formigenes may have in that association.

METHODS

We performed a MEDLINE search of "cystic fibrosis and nephrolithiasis" and "Oxalobacter formigenes." Epidemiological and experimental evidence and possible mechanisms explaining the association were critically reviewed.

RESULTS

Of patients with CF, 3.0% to 6.3% are affected with nephrolithiasis, a percentage greater than that of age-matched controls without CF, in whom the rate is 1% to 2%. Studies have suggested possible mechanisms for the association, including hyperuricosuria, hyperoxaluria, primary defects in calcium handling caused by mutation of the CF transmembrane regulator (CFTR), hypocitraturia, and lack of colonization with O formigenes, an enteric oxalate-degrading bacterium. The absence of colonization could be related to frequent courses of antibiotics.

CONCLUSION

Although the incidence of stones in patients with CF may be increased compared with controls without CF, many possible mechanisms are implicated. The relative contributions of these mechanisms remain uncertain. Future directions may include specific identification of lithogenic risks and therapy aimed at stone prevention in this population.

Intestinal Oxalobacter formigenes colonization in calcium oxalate stone formers and its relation to urinary oxalate

BACKGROUND AND PURPOSE

Oxalobacter formigenes is an anaerobic commensal colonic bacterium capable of degrading oxalate through the enzyme oxalyl-CoA decarboxylase. It has been theorized that individuals who lack this bacterium have higher intestinal oxalate absorption, leading to a higher urinary oxalate concentration and an increased risk of calcium oxalate urolithiasis. We performed a prospective, controlled study to evaluate O. formigenes colonization in calcium oxalate stone formers and to correlate colonization with urinary oxalate and other standard urinary stone risk factors.

PATIENTS AND METHODS

Thirty-five first-time calcium oxalate stone formers were compared with 10 control subjects having no history of urolithiasis and a normal renal ultrasound scan. All subjects underwent standard metabolic testing by submitting serum and 24-hour urine specimens. In addition, all subjects submitted stool samples for culture and detection of O. formigenes by Xentr(ix) O. formigenes Monitor.

RESULTS

Intestinal Oxalobacter was detected in only 26% of the stone formers compared with 60% of the controls (p < 0.05). Overall, the average urinary oxalate excretion by the two groups was similar (38.6 mg/day v 40.8 mg/day). Among stone formers, however, there were statistically higher urinary oxalate concentrations in O. formigenes-negative patients compared with those testing positive (41.7 mg/day v 29.4 mg/day) (p = 0.03). Furthermore, all 10 stone formers with hyperoxaluria (>44 mg/day) tested negative for O. formigenes (p < 0.05).

CONCLUSIONS

Calcium oxalate stone formers have a low rate of colonization with O. formigenes. Among stone formers, absence of intestinal Oxalobacter correlates with higher urinary oxalate concentration and an increased risk of hyperoxaluria. Introduction of the Oxalobacter bacterium or an analog of its enzyme oxalyl-CoA decarboxylase into the intestinal tract may be a treatment for calcium oxalate stone disease.

Detection and identification of oxalate-degrading bacteria in human feces

BACKGROUND

Oxalate is detoxified (catabolized) via the action of two enzymatic proteins, formyl coenzyme A transferase (encoded by the frc gene) and oxalyl coenzyme A decarboxylase (encoded by the oxc gene), contained in the cytosol of Oxalobacter formigenes that colonizes the human intestinal tract. It is speculated that oxalate-degrading bacteria decrease oxalate absorption from the intestines and their absence in the gastrointestinal tract correlates with the formation of calcium-oxalate urolithiasis.

METHODS

Two methods of detection and identification of this bacterial strain were studied in human fecal samples collected from Japanese subjects. Genomic DNA was isolated from bacterial culture, and specific 16S rDNA was amplified by polymerase chain reaction (PCR) followed by sequencing. The oxc gene was amplified directly from human feces by PCR using the specific primers.

RESULTS

Oxalate-degrading bacteria were identified by comparing the sequences of 16S rDNA. The oxc gene was directly detected from human feces by PCR. It was ascertained that a combined PCR detection method using both 16S rDNA and the oxc gene allows for identification of O. formigenes in human fecal samples.

CONCLUSION

This detection and identification method of oxalate-degrading bacteria using 16S rDNA and oxc gene should be applied in examination of clinical samples.