Kidney stones have plagued people for millennia. They cause excruciating pain and can lead to serious complications, especially when proper medical care is lacking. So any new information about kidney stones matters a lot.
An interdisciplinary team behind a new study found live bacteria and biofilms inside the most common type of stones — those made of calcium oxalate (oxalate stones). These account for about 80 percent of all cases. Until now, scientists thought these stones were made entirely of minerals that crystallized from salts in the urine.
The team found that bacteria aren’t just present in oxalate stones — they actively participate in their formation.
“This scientific breakthrough overturns the long-held assumption that these stones form solely through chemical and physical processes; it’s clear that bacteria can live inside the stones and actively contribute to their formation,” said urologist Kimora Scotland, the study’s lead author.
What scientists found about bacteria inside common kidney stones
Stone formation begins with the nucleation and growth of tiny crystals from supersaturated urine. Medical science has found some ways to suppress that process, Science Alert reported.
“Nucleation and crystal growth are complex processes in which many factors can act as either catalysts or inhibitors, depending on the local environment and the physical properties of the molecule,” the team wrote in their report.
Urologists already knew that bacteria are involved in forming so-called struvite kidney stones, which are relatively rare and make up about 2–6 percent of cases. But no one suspected that microbes played a role in forming the much more common oxalate stones.
Using electron and fluorescence microscopy, the researchers didn’t just find a few bacteria attached to the surface of a calcium stone. They found live bacteria and even biofilms embedded inside the crystals that make up the stones.
“We identified a previously unknown mechanism of stone formation that helps explain why these stones are so common,” Scotland said.
She said bacteria may help stones form in the kidney and then become trapped in the new structure, around which additional crystals aggregate.
The researchers suggest treating kidney stones as an “organic–inorganic biocomposite” whose key component is bacterial biofilms — even in cases where routine clinical tests don’t detect bacteria.
This finding has implications for the health of tens of millions of people worldwide. But the team needs additional research to fully clarify the role bacteria play in stone formation.
“We want to understand exactly why some patients are especially prone to recurrent stones, and what allows particular bacterial species to form stones,” Scotland emphasized.
The study’s conclusions were published in the journal PNAS.
