Live Bacteria Found Inside Kidney Stones & It Could Rewrite How Doctors Treat Them

Kidney stones have caused human suffering for thousands of years. Ancient Egyptian mummies have been found with them. Medical texts dating back to 600 BC describe their symptoms. And yet, for all that history, a team of researchers in Los Angeles has just discovered something about the most common type of kidney stone that nobody had ever noticed before. What they found buried inside those mineral deposits may rewrite how medicine understands, treats, and prevents one of the most painful conditions on the planet.

A Condition That Never Goes Away

Before getting to what scientists found, it helps to understand the scale of the problem they were studying. About 1 in 11 people will develop a kidney stone at some point in their lifetime, and that rate has been climbing globally for decades. Risk factors range from family history and metabolic syndrome to something as straightforward as not drinking enough water. For many patients, a first stone is also far from the last. Recurrence rates reach as high as 80% in certain stone types, a figure that has left doctors and patients alike searching for answers that standard treatment has never fully provided.

Kidney stones form when crystals grow in urine and become large enough that normal fluid flow can no longer wash them out. Calcium oxalate stones, by far the most prevalent variety, account for nearly 80% of all cases worldwide. For decades, medical science treated them as straightforward mineral buildups, chemical events driven by elevated concentrations of calcium and oxalate in urine. Diet changes, hydration, and in stubborn cases, surgery were the primary tools available. For millions of people, those tools were never quite enough.

What a UCLA Lab Found in January 2026

A research team led by UCLA published findings in January 2026 in the Proceedings of the National Academy of Sciences, one of the most respected peer-reviewed journals in science, that upended that long-standing picture.

Using electron microscopy and fluorescence microscopy, the team examined calcium oxalate kidney stones collected from human patients. What they expected to find was a mineral structure. What they actually found were live bacteria and layers of bacterial biofilm woven into the interior of the stones, not clinging to the outer surface, but embedded deep within the crystalline architecture itself.

“This breakthrough challenges the long-held assumption that these stones develop solely through chemical and physical processes, and instead shows that bacteria can reside inside stones and may actively contribute to their formation,” said Dr. Kymora Scotland, an assistant professor of urology at the David Geffen School of Medicine at UCLA and the study’s co-senior author. “By uncovering this novel mechanism, the study opens the door to new therapeutic strategies that target the microbial environment of kidney stones.”

Calcium oxalate stones had never been known to contain bacteria. A rare stone type called struvite, sometimes referred to as an infection stone, had a documented bacterial connection, but it represents only 2 to 6% of cases. Calcium oxalate stones were classified as noninfectious. Doctors operated on that assumption for generations. As of January 2026, that classification no longer holds.

Bacteria as Architects, Not Passengers

Finding bacteria inside kidney stones would be striking enough on its own. What makes the UCLA study particularly consequential is what the researchers believe those bacteria are actually doing.

Based on their evidence, bacteria do not simply end up trapped inside stones by accident. Instead, they appear to play an active role in building them. Researchers propose that bacteria act as seeds, providing surfaces on which calcium oxalate crystals begin to accumulate and grow. As mineral layers build up around the bacterial colonies, the bacteria become locked inside the developing stone structure. Over time, more crystal layers form on top, burying the bacteria deeper within a hardening mineral shell.

Supporting this model, the team found that calcium oxalate crystal domains located near bacterial layers were measurably smaller than those found elsewhere in the stone. Smaller crystal domains indicate a higher concentration of nucleation sites, exactly what you would expect if bacteria and their secreted DNA were actively drawing in calcium ions and triggering crystal formation at an accelerated rate.

Bacterial DNA released outside the cell walls appears to function as a kind of molecular scaffold. DNA carries a dense negative charge, which attracts and concentrates calcium ions from the surrounding urine environment. Urine, especially in people prone to kidney stones, can carry calcium concentrations up to 7 millimoles per liter, a level that places enormous metabolic pressure on bacteria trying to maintain their own internal calcium balance. Researchers suggest that in response, bacteria release anomalously large amounts of extracellular DNA into the urine environment, and that DNA becomes a powerful template for crystal nucleation. “We found a new mechanism of stone formation that may help to explain why these stones are so common,” Scotland said.

Why Standard Tests Kept Missing All of This

A reasonable question follows from this finding. If bacteria are present inside calcium oxalate kidney stones, why has clinical testing missed them for so long? Part of the answer lies in how medical labs test for bacterial presence. Standard clinical culture testing works by homogenizing stone fragments, then growing any released bacteria on selective media. It is a method built around the assumption that bacteria, if present, will be culturable using conventional techniques. That assumption turns out to be flawed in this setting.

Researchers estimate that roughly 99% of bacteria found in nature cannot be cultured using standard laboratory methods. Some species have complex growth requirements that standard media cannot replicate. Others exist in what scientists call a viable but nonculturable state, a kind of low-metabolic dormancy in which the cells are alive but not actively replicating. Bacteria sheltering inside kidney stones appear to occupy exactly this kind of state, protected from both standard culture detection and from the body’s immune system by layers of mineral and biofilm.

Biofilm itself adds another layer of protection. Bacterial biofilm is a structured community of microorganisms encased within a self-secreted matrix of polysaccharides and extracellular DNA. That matrix acts as a shield, making the bacteria inside far more resistant to external threats than free-floating cells would be. Inside the layered structure of a kidney stone, a biofilm colony can persist in a protected state that clinical tests are not designed to detect.

To get around these limitations, the UCLA team used a combination of advanced imaging and chemical analysis methods borrowed from materials science, scanning electron microscopy, focused ion beam sectioning, fluorescence confocal imaging, and targeted chemical staining. Bacteria and biofilm components turned up consistently, even in stones that had tested culture-negative in clinical settings.

Recurring Infections, Recurring Stones

For patients who have spent years cycling through kidney stone episodes and urinary tract infections, the UCLA findings offer a possible explanation that medicine has never had before.

If bacteria live inside kidney stones, those bacteria do not simply disappear when a stone is broken up during treatment. Procedures like lithotripsy, which use sound waves to fragment stones, may actually release previously sheltered bacteria into the urinary tract. Once freed from their mineral casing, those bacteria enter an environment where, given enough time to recover from their dormant state, they may be capable of growth, replication, and infection.

More than 30% of stones analyzed in the study showed polymicrobial colonization, meaning multiple bacterial species had taken up residence within a single stone. Species identified included Escherichia coli, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus epidermidis, organisms well known to clinicians for their roles in urinary tract infections. Finding them inside stones that standard testing had labeled noninfectious raises immediate questions about how post-procedure infections should be understood and managed.

What This Could Mean for Treatment

Right now, treatment options for calcium oxalate stones are narrow. Patients are advised to change their diets, drink more fluids, and, in cases where stones grow too large or cause obstruction, undergo surgical removal. Antibiotics have been used in managing recurrent struvite infection stones, but that approach carries a genuine risk of antibiotic resistance and has not historically been applied to calcium oxalate stones, which were not considered infectious.

If bacteria are a contributing factor in how calcium oxalate stones form and recur, that treatment picture changes. Therapies aimed at preventing biofilm formation, disrupting bacterial colonization in the urinary environment, or clearing dormant bacteria before they can seed new crystal growth could become meaningful clinical tools. For the tens of millions of people worldwide who have seen dietary adjustments and hydration do little to stop their stones from coming back, that possibility represents a genuine shift in what medicine might eventually offer them.

The Questions That Still Need Answers

Scotland and her team have been careful to frame this discovery as a beginning rather than a conclusion. Much about the relationship between bacteria and calcium-based kidney stones remains poorly understood, and the study’s authors are clear that more research is needed before any new treatment protocols can follow from their findings.

For one, the study focused on calcium-based stones. Whether bacteria play similarly overlooked roles in other, less common stone types is a question the researchers have flagged but not yet answered. For another, the precise mechanisms by which bacterial colonization leads to stone nucleation and growth are still being worked out. Follow-up studies are currently underway within the research team’s multi-institutional collaboration.

“We want to understand exactly what makes some patients particularly susceptible to recurrent stone formation, and what it is about these particular species of bacteria that allows them to nucleate these stones,” Scotland said.

A Long-Standing Problem, A New Set of Questions

Kidney stones have been a fixture of human medical history for millennia. Countless patients have passed them, had them removed, and then watched as new ones formed despite every precaution. For many of them, the explanation has always been incomplete, a matter of diet, hydration, and bad luck.

What the UCLA team has put forward is a different kind of explanation, one that places living organisms at the center of a process medicine had long considered purely chemical. Whether that explanation holds up across further study, and whether it eventually produces treatments that break the cycle of recurrence for millions of patients, remains to be seen. But for a condition as old as recorded medicine, finding something that nobody had ever looked for, and finding it hiding inside the stones themselves, is a significant place to start.

Source: Schmidt, W. C., Mousavi, A., Li, J., Yang, R., Marin, G. G., Schreiber, H. L., Hammann, R. E. S., Obernuefemann, C. L. P., Bergeron, K., Klim, A., Wong, D., Du, K., Hultgren, S. J., Chen, Q., Celestian, A., Wong, G. C. L., & Scotland, K. B. (2026). Intercalated bacterial biofilms are intrinsic internal components of calcium-based kidney stones. Proceedings of the National Academy of Sciences, 123(5), e2517066123. https://doi.org/10.1073/pnas.2517066123