Intestinal bacteria infiltrate the brain after implantation of medical devices

The hope of brain implants can help patients with paralysis, epilepsy and other neurological diseases get complicated by the unexpected culprit: bacteria in the gut may invade the brain after implantation.

Scientists at Case Western Reserve University recently discovered that when medical devices are implanted into the brain, they can cause damage in the blood-brain barrier, allowing bacteria, a type of bacteria from the gut, to enter brain tissue. This bacterial invasion can cause inflammation, and over time, the implants are less effective.

“This is a discovery of paradigm change,” said George Hoeferlin, lead author of the study. “For decades, the field has focused on the body’s immune response to these implants, but our study now shows that some bacteria derived from the gut also play a role in inflammation around these devices.”

The study, published in Natural Communications in March 2025, could change the way brain implants are designed and maintained, making them more effective for patients who rely on the technology to restore neurological function.

The brain-machine interface is increasingly used to help patients with paralysis, such as controlling external devices or even their own limbs. However, maintaining long-term reliability has been a major challenge. So far, researchers have mainly blamed the body’s immune response on the gradual decline in device performance.

The study examined the presence of bacterial DNA in the brains of mice implanted with microelectrodes. The researchers found that devices treated with antibiotics reduced bacterial contamination and improved performance at least temporarily. However, long-term use of antibiotics has proven to be harmful.

“Understanding the role of bacteria in implant performance and brain health may revolutionize the way these devices are designed and maintained,” said Jeff Capadona, vice provost for innovation at Case Western Reserve, a senior research career scientist at Donnell Institute and a senior research career scientist at Louis Stokes Stokes Stokes Cleveland Va Medical Center.

The team used advanced sequencing techniques to identify bacterial DNA in brain tissue around the implant, with many sequences matching bacteria commonly found in the intestine. In mice treated with antibiotics to reduce gut bacteria, the implant initially performed better, with less inflammation around the device.

The study provides a new perspective on why brain implants often fail over time. The results show that implanted trauma creates channels for bacteria to enter the brain, triggering an inflammatory response, which interferes with the device’s ability to detect neural signals.

Even more worryingly, some of the bacteria found in the brain have been associated with neurological diseases including Alzheimer’s, Parkinson’s, and stroke.

“If we do not identify or address the results of the implant, we may cause greater harm than we solve,” Capadona added. “This finding highlights the urgent need to develop permanent strategies to prevent bacteria from invading from implanted devices, rather than just managing inflammation after the fact, and the more we know about the process, the more efficient we can design the implant.”

The team also examined the feces of human subjects who were implanted with brain devices and found similar bacterial patterns, suggesting that this is not only a laboratory phenomenon, but may also be a clinically relevant problem that may affect patients with neural implants.

“Through our strong translation pipeline between CWRU and VA, we are now investigating how this discovery can directly contribute to a safer and more effective neural implant strategy for patients,” said Bolu Ajiboye, Robert and Brenda Aiken, professor of biomedical engineering in the field of biomedical engineering at the Elville Delanshire School of Engineering and Scientists’ Case School.

In their study, scientists not only identified bacterial invasion, but also observed how it disrupts the gut axis, resulting in reduced microelectrode performance. While short-term antibiotic treatment improves implant function, long-term use is associated with neurodegenerative pathways and deteriorates performance, which is a need for more targeted approaches.

The discovery opens potential avenues for potential new avenues to improve brain implantation techniques, including designing antibacterial coatings for devices or developing preventive therapies that are specifically targeting problematic bacteria without destroying beneficial microorganisms.

Capadona’s lab is now expanding research to examine bacteria in other types of brain implants, such as ventricular shunts used to treat hydrocephalus, which are abnormal accumulation of fluid in the brain.

With the continuous development of brain implantation technology, this study provides a critical new understanding of the biological challenges faced by these devices and has the potential to overcome them.