Urological diseases such as urinary tract infections (UTI) and kidney stones are a serious burden and are considered the twelfth leading cause of death and seventeenth of disability. Recent work has revealed that the urinary tract is also not free of bacteria in healthy people. But while research has suggested that there are bacteria in the kidney, there has not been direct evidence to support this idea. In a new study, scientists wanted to know whether there are resident bacteria in the kidney, how they affect kidney health, and how they might be affected by antibiotics that are often used to treat kidney diseases.
In this work, the researchers used a mouse model to reveal the presence of bacteria in the kidney and understand how they are affected by antibiotics. They also confirmed that there are low levels of bacteria in healthy human kidneys as well. The findings have been reported in Nature Communications.
The investigators identified certain strains of bacteria in the kidney microbiome that are able to influence the development of kidney stones; some prevented the kidney stones while others promote them. The bacterium E. coli was linked to the presence of kidney stones, while another microbe called Lactobacillus crispatus was associated with the lack of kidney stones.
The study showed that the misuse of antibiotics, when they are applied to situations where they are not needed, can alter the kidney microbiome to favor the stone-boosting bacteria.
"Urologic diseases like kidney stones impact 63 percent of the adult population and are getting worse," noted senior study author Aaron Miller, PhD. "The data consistently points towards bacteria. If we can't get over the assumption of sterility, we can't develop more effective treatments and preventative options."
True microbiomes are considered to have a few characteristics: the bacteria must be metabolically active, the microbiome must be stable, consistent, and reproducible. In this study, all of those characteristics were confirmed. The bacteria in the kidney microbiome and urinary tract were also not related to disease, the study authors noted. They were identified in people without any symptoms of urological diseases.
The team also developed a system to ascertain whether bacteria can affect the formation of kidney stones. A chamber was built to mimic urine movement through kidneys, with the added ingredients of calcium and oxalate, which make up kidney stones.
The researchers saw crystals forming, like stones, in chambers where E. coli was present. These crystals were found to be just like human kidney stones. But in the Lactobacillus chambers, no stones formed.
When the microbes were combined in a similar testing chamber, crystals formed but they were unlike kidney stones, which seems to suggest that Lactobacillus can prevent the ability of E. coli to boost stone formation.
When antibiotics were applied to this situation, the microbial balance moved away from Lactobacillus to create an environment that is more conducive to stone formation. It may explain why long-term antibiotic use can promote kidney stones.
Now the researchers want to know more about how this work can be applied to help diagnose or treat patients.
"If the kidney microbiome can influence kidney stones, it can likely influence other kidney diseases as well. We are already looking at microbial signatures for other kidney diseases and have even submitted a grant to investigate how certain genetic variants influence the renal microbiome and kidney disease risk in different ethnicities," added Miller.
Sources: Cleveland Clinic, Nature Communications