Microbiome: Kidney Stones and Gut Bacteria

Kidney stones are predominantly composed of calcium oxalate (CaOx) derived from both endogenous and exogenous sources affecting 1 in 11 people in the United States. It is a multifactorial disorder with a complex interaction between gut, liver, bone, and kidney that the underlying mechanisms are complex. There are different types of surgical and lithotripsy interventions available for immediate treatment. However, given the chronic nature of the disease with stone recurrence in many patients, novel therapeutic approaches are necessary. One approach to prevent renal stone recurrence is to decrease consumption of oxalate-rich foods. However, the recent concept of reducing oxalate absorption by a microbiological approach has been increasing attention.

What is the bacteria that is clinically significant of kidney stones?

Oxalobacter formigenes, a Gram-negative, anaerobic bacterium colonization metabolizing oxalate in the intestinal tract and is present in a large proportion of the normal adult population.

How is the bacteria related to kidney stones?

Oxalobacter formigenes colonization has a strong inverse association with CaOx nephrolithiasis, with a 70% reduction in overall risk. O. formigenes induces fecal oxalate excretion by enhancing secretion into colon and thereby to normalize urinate oxalate excretion. Thus, in the absence of O. formigenes, net intestinal oxalate absorption could increase, resulting in higher plasma and urinary oxalate levels and risk of stone development.

What are the symptoms of kidney stones?

• Severe pain in the side and back, below the ribs
• Pain that radiates to lower abdomen and groin and/or comes in waves and fluctuates in intensity
• Painful/frequent urination
• Pink, red or brown, cloudy or foul-smelling urine
• Nausea and vomiting

How do you determine the levels of the bacteria?

Our office can provide a stool test to analyze the microbiome of the patient. Indications for the testing include:

• History of calcium oxalate kidney stone
• Family history of calcium oxalate kidney stones
• History of antibiotics use (within 5 years) of which O. formigenes is sensitive including: azithromycin, ciprofloxacin, clarithromycin, clindamycin, doxycycline, gentamicin, levofloxacin, metronidazole, and tetracycline

What are some interventions to consider?

• Low oxalate diet: avoid oxalate rich foods such as spinach, rhubarb, beets, potato chips, nuts and nut butters, miso soup, grits, cocoa powder, okra
• Probiotic with formigenes: increase the number of bacteria in the gut
• Low fat diet: limit the effects of bile acids on oxalate absorption in the colon
• Low calcium supplement intake: excessive calcium supplement intake has been found to increase kidney stone risk
• Avoid antibiotics to which formigenes is known to be sensitive (refer above)
• Check a bone density scan: low levels of formigenes is associated with decreased bone mineral density

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