Scientists have discovered for the first time that even so-called non-infectious kidney stones can contain bacteria. The finding concerns calcium oxalate stones—the most common type of kidney stones. The study was conducted by a team of researchers from the University of California, Los Angeles, and published in the journal Proceedings of the National Academy of Sciences (PNAS).

Kidney stones have traditionally been considered the result of purely chemical and physical processes, such as high concentrations of salts and minerals in urine and insufficient fluid intake. After such stones pass, physicians usually do not view them as being related to infection. However, the new data call this assumption into question.

Using electron and fluorescence microscopy, the researchers examined calcium oxalate stones removed from patients and identified clusters of bacteria within their structure. The microorganisms were embedded in the internal “architecture” of the stones in the form of layers and biofilms. This was observed even in patients who had not been diagnosed with urinary tract infections.

“This discovery challenges the long-held belief that these stones form solely due to chemical and physical factors. We have shown that bacteria can hide inside stones and may actively participate in their formation,” explained Kimora Scotland, a urologist at the University of California.

According to the study’s authors, the presence of bacteria may partly explain why kidney stones recur in some people despite treatment and lifestyle changes. In such cases, the underlying cause may be a hidden bacterial infection in the kidneys, ureters, or bladder.

“We have identified a new mechanism of stone formation that helps explain why they are so widespread. This may also clarify the link between recurrent urinary tract infections and repeated stone formation,” Kimora Scotland noted.

Statistics show that approximately one in eleven people experiences kidney stones at least once in their lifetime, and more than 70% of cases are associated specifically with calcium oxalate stones. If further research confirms the key role of bacteria, approaches to the prevention and treatment of kidney stone disease may change, placing greater emphasis on the microbial environment and hidden infections.

The authors emphasized that their findings open the door to new therapeutic strategies aimed not only at the chemical composition of urine, but also at controlling bacterial processes occurring within the kidneys.

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