Bacteria can reside inside stones and actively drive their formation
For generations, kidney stones were understood as a purely chemical affliction — minerals crystallizing in silence, indifferent to life. A team of UCLA researchers has now found that life, in the form of bacteria woven into the very architecture of the stones, may have been there all along. Their discovery, published in PNAS, suggests that the most common kidney stones are not merely geological formations within the body, but microbial constructions — a finding that quietly redraws the boundary between chemistry and biology in human disease.
- Bacteria and biofilms were found embedded inside 80% of calcium oxalate kidney stones — not on the surface, but structurally integrated, as if the stone itself were built around them.
- This overturns decades of medical consensus: a condition affecting 1 in 11 people globally, long treated as a chemistry problem, may have a hidden microbial engine driving it.
- The discovery casts new light on a stubborn clinical mystery — why patients with recurrent urinary tract infections so often suffer recurrent kidney stones, suggesting the same bacteria may be responsible for both.
- Researchers from UCLA, the University of Illinois, Washington University, and the Natural History Museum of Los Angeles are now racing to identify which bacterial species nucleate stones and why some patients are especially vulnerable.
- If bacteria are confirmed as architects of stone formation, entirely new therapies targeting microbial biofilms — rather than urinary chemistry alone — could reach patients who have never had effective prevention options.
Kidney stones have long been treated as a chemistry problem — minerals crystallizing in urine until they grow too large to pass. A UCLA research team has now found something that changes that picture entirely. Using electron and fluorescence microscopy, they discovered living bacteria arranged in biofilms embedded directly within the crystal structure of calcium oxalate stones, the most common type, which account for nearly 80 percent of all cases.
The bacteria were not surface contaminants. They were woven into the stone's architecture, suggesting they may actively participate in stone formation rather than simply appearing afterward. Dr. Kymora Scotland, assistant professor of urology at UCLA's David Geffen School of Medicine and co-senior author of the study, describes the implications as substantial — the findings open the door to therapeutic approaches that target the microbial environment itself, not just the chemistry of crystallization.
The discovery may also explain a long-observed clinical puzzle: why recurrent urinary tract infections so often accompany recurrent kidney stone formation. If bacteria are integral to how stones develop, the same species driving infections may also be nucleating stones — a connection that could reshape prevention strategies for patients vulnerable to both conditions.
Kidney stones affect roughly one in eleven people over their lifetime, and prevalence is rising globally. The research team, which includes collaborators from the University of Illinois, Washington University, and the Natural History Museum of Los Angeles, is now investigating which bacterial species are capable of nucleating stones and whether microbes play a role in less common stone types as well. The work, supported by the NIH and NSF, will be published in PNAS — and for the millions who know kidney stones as among the most painful experiences in medicine, it may mark the beginning of a genuinely new era of treatment.
Kidney stones have long been understood as a purely chemical problem—minerals crystallizing in the urine, accumulating until they become too large to pass. A UCLA research team has upended that assumption. Using electron and fluorescence microscopy to examine the most common type of kidney stone, they found something unexpected: living bacteria, arranged in layers called biofilms, embedded directly within the crystal structure itself.
The discovery challenges decades of medical understanding. Calcium oxalate stones, which account for nearly 80 percent of all kidney stone cases, were never thought to harbor bacteria. Yet there they were—not contaminating the surface, but woven into the stone's architecture. The finding suggests that bacteria may actively participate in stone formation rather than simply appearing after the fact, opening a fundamentally different way of thinking about how these painful deposits develop.
Kidney stones affect roughly one in eleven people over their lifetime, and the prevalence has been climbing globally. They form when crystals in the urine grow large enough that normal urination cannot flush them away. Risk factors include family history, metabolic syndrome, and insufficient fluid intake. The condition is common enough that it represents a significant public health concern, yet until now, the role of microbes in the most prevalent stone type remained completely unknown.
Dr. Kymora Scotland, an assistant professor of urology at UCLA's David Geffen School of Medicine and a co-senior author of the study, describes the implications as substantial. The research reveals that bacteria can reside inside stones and may actively drive their formation—a mechanism that contradicts the long-held belief that these stones develop solely through chemical and physical processes. This reframing opens the door to entirely new therapeutic approaches: instead of only addressing the chemistry of stone formation, doctors might target the microbial environment itself.
The findings may also illuminate a long-observed clinical puzzle: why recurrent urinary tract infections so often accompany recurrent kidney stone formation. If bacteria are integral to stone development, the connection becomes less mysterious. A patient prone to infections may be particularly vulnerable to stone recurrence because the same bacterial species that cause infections may also nucleate stone formation. Understanding this link could reshape how doctors approach prevention and treatment for patients with a history of either condition.
The research team, which includes collaborators from the University of Illinois, Washington University, and the Natural History Museum of Los Angeles, emphasizes that much work remains. The study focused specifically on calcium-based stones. Researchers are now investigating exactly which bacterial species are capable of nucleating stones, why some patients are particularly susceptible to recurrence, and whether bacteria play a role in other, less common stone types. Scotland notes that the findings suggest bacteria could be involved in stone formation more broadly than previously recognized.
The work, to be published in the peer-reviewed journal PNAS, was supported by grants from the National Institutes of Health, the National Science Foundation, and other federal and private sources. For the millions of people who experience kidney stones—often described as among the most painful medical conditions—the discovery of this hidden bacterial component represents a potential turning point. If bacteria are indeed central to stone formation, then therapies designed to disrupt or prevent bacterial biofilm development could offer new paths to prevention and treatment that have never been available before.
Citações Notáveis
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.— Dr. Kymora Scotland, UCLA assistant professor of urology
We found a new mechanism of stone formation that may help to explain why these stones are so common and may also help explain the connections between recurrent urinary tract infections and recurrent kidney stone formation.— Dr. Kymora Scotland
A Conversa do Hearth Outra perspectiva sobre a história
So bacteria were just sitting inside these stones the whole time, and nobody noticed?
Not exactly. The stones were being studied, but researchers were looking for chemical and mineral explanations. The microscopy technology and the specific focus on biofilms made the difference—they were looking in a way that revealed what was actually there.
Does this mean every kidney stone has bacteria in it?
Not necessarily. This study focused on calcium oxalate stones, which are the most common type. But the researchers suspect bacteria may play a role in other stone types too. That's part of what they're investigating next.
If bacteria cause the stones, why doesn't antibiotics just solve the problem?
That's the key question they're trying to answer now. Bacteria embedded in biofilms behave differently than free-floating bacteria. They're protected, organized, harder to reach. Understanding which species are involved and how they interact with the stone chemistry is essential before you can design an effective treatment.
What about people who keep getting stones over and over?
That's where the urinary tract infection connection becomes interesting. If the same bacteria that cause infections also nucleate stones, then a patient with recurrent infections might be caught in a cycle. Breaking that cycle could require targeting the bacteria themselves, not just treating the chemical imbalance.
So this changes how doctors should think about prevention?
Potentially, yes. Instead of only focusing on hydration and diet to manage the chemistry, doctors might eventually be able to identify which patients carry stone-forming bacteria and intervene at that level. That's still years away, but the mechanism is now visible.