Previously unknown bacterial component in kidney stone formation discovered

In an unexpected finding, a research team has discovered that bacteria are present inside the most common type of kidney stone, revealing a previously unrecognized component involved in their formation.
Bacteria have been identified within calcium oxalate kidney stones, indicating a previously unrecognized microbial role in their formation. This challenges the view that these stones arise solely from chemical and physical processes and suggests that targeting bacterial biofilms could offer new prevention and treatment strategies for kidney stone disease.

The findings, to be published in the journal Proceedings of the National Academy of Sciences, point to a possible therapeutic target that could be used for prevention and treatment for the millions of people who are affected by the frequently painful condition.

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.

Kidney stones are composed of clumps of small crystals. Their prevalence has risen globally in recent years, so that today about 1 in 11 people will get them in their lifetime. Risk factors include family history, metabolic syndrome, and low fluid intake. The stones start forming when crystals grow in urine and become large enough that they can't be washed out with normal urine flow.

There are several subsets of kidney stones and while one rare stone type is known to contain bacteria, by far the most common stone is calcium oxalate (CaOx), comprising almost 80% of kidney stone cases, which have not been previously known to contain bacteria. While examining data from electron and fluorescence microscopy, the researchers unexpectedly detected live bacteria as well as layers, or biofilms, of bacteria integrated into the crystals.

Researchers found a new mechanism of stone formation that may help to explain why these stones are so common.

These results may also help to explain the connections between recurrent urinary tract infections and recurrent kidney stone formation, and provide insights on potential future treatment for these conditions. The findings suggest that bacteria could also be involved in other kidney stone types.

The study focused on calcium-based stones. How other less common stones form is still in question. More studies are needed to fully understand how bacteria and calcium-based kidney stones interact, the researchers conclude.

Wong, Gerard C. L. et al, Intercalated bacterial biofilms are intrinsic internal components of calcium-based kidney stones, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2517066123. doi.org/10.1073/pnas.2517066123